Mashiro's Journey: From Kep1er to MADEIN - Everything Fans Need to Know

Mashiro recently made headlines when she transitioned from K-pop girl group Kep1er to her new home at MADEIN. After placing 8th in the finals of Girls Planet 999 with 708,149 points, Sakamoto Mashiro debuted as co-leader of Kep1er on January 3, 2022, with their first mini album "First Impact". During her time with the group, Mashiro Kep1er served as vice-leader from January 2022 until July 15, 2024, when she officially concluded her activities following the group's scheduled Japanese concert. Following the announcement on May 30, 2024, that she would not renew her contract, Mashiro subsequently joined MADEIN under 143 Entertainment, marking an exciting new chapter in her career.

Early Life and Background

Born in Tokyo, Japan, Sakamoto Mashiro's journey to K-pop stardom began far from the spotlight. As an only child, Mashiro grew up in a supportive household that would eventually nurture her artistic ambitions. Her family home in Tokyo also included two pet cats, companions that would remain dear to her heart throughout her career.

Birthplace and family

Mashiro's Japanese roots remain an important part of her identity. Growing up in Tokyo shaped her early perspectives and provided the foundation for her later multicultural career. Unlike many K-pop idols with siblings, Mashiro navigated her childhood as an only child, perhaps contributing to her independent spirit. Before venturing into the K-pop world, she gained valuable experience as both a model and actress in her home country, developing performance skills that would later serve her well.

First exposure to K-pop

Mashiro's fascination with K-pop began unexpectedly through a Korean drama. At the age of 12, her mother recommended she watch "Dream High," a series that would ultimately change the course of her life. The drama, which followed students pursuing their dreams of becoming idols, captivated the young Mashiro while she was in fifth grade of elementary school.

"After watching 'Dream High', I fell in love with K-pop," Mashiro explained in a later interview. "In terms of music, I felt that K-pop was something I could be active in on a more global scale, and I was drawn to it". The show's portrayal of aspiring performers learning to dance and sing struck her as fascinating and somewhat magical.

Additionally, Mashiro became particularly interested in Miss A, the girl group that featured actress Bae Suzy, who starred in "Dream High". This initial exposure planted the seed for what would eventually become her career path.

Initial dreams of becoming an idol

The dream that began while watching Korean entertainment soon transformed into concrete action. Mashiro recalled, "I've begun dreaming of becoming an idol after watching the Korean drama 'Dream High' in elementary school". The appearance of art high school students training in dance and singing represented an exciting fantasy world to her young eyes.

By the time she turned 16 in 2016, Mashiro had made the life-changing decision to pursue her dreams in South Korea. This bold move demonstrated remarkable determination for a teenager, especially considering she would need to adapt to a new country and language.

Upon arriving in Korea, Mashiro quickly discovered she faced unique challenges. "Since there were no Japanese trainees at the time, she studied Korean diligently for communication and almost 'to survive'," according to reports. Her dedication paid off remarkably soon thereafter.

Mashiro's first major achievement came through JYP Entertainment's 12th audition show, where she impressed the judges with both her visual appeal and talent. Among many competitors, she finished in second place - an outstanding accomplishment that earned her a coveted trainee contract with one of Korea's most prestigious entertainment companies. This marked the official beginning of her journey toward becoming a K-pop idol, though her path would include several unexpected turns before reaching her eventual debut.

Training Years Before Debut

In 2016, Mashiro began her formal K-pop training journey, embarking on a path filled with both promising opportunities and unexpected challenges. After passing JYP Entertainment's 12th annual public audition with an impressive second-place finish, her trainee life officially commenced.

JYP Entertainment journey

Mashiro made history at JYP Entertainment as the first foreigner to travel to Korea, audition in person, and successfully secure a trainee position. This remarkable achievement demonstrated her exceptional talent and determination. Throughout her two-year tenure at JYP from 2016 to 2018, Sakamoto Mashiro trained alongside several trainees who would eventually become members of ITZY—including Yeji, Ryujin, Chaeryeong, and Yuna.

Her time at JYP included notable public appearances, such as participating in the female trainee showcase on the JYP reality show "Stray Kids". After the showcase performance, JYP founder Park Jin-young reportedly commented that "the women's two teams were more noticeable" than the male trainees. Furthermore, Mashiro was part of the pre-debut group known as "Girls 2TEAM" at JYP Entertainment, where she continued developing her skills and building relationships with fellow trainees.

Despite her obvious talents and hard work, Mashiro was not selected for the final ITZY lineup when the group was formed. This decision marked a difficult turning point in her journey.

Pledis and Stone Music trainee period

After departing JYP Entertainment in 2018, Mashiro continued pursuing her dreams by joining Pledis Entertainment for a brief period. During this time, she became involved in an exciting collaborative project between Stone Music Entertainment and Pledis.

Notably, Mashiro was planned to debut in a girl group formed through this collaboration, alongside Lee Gaeun, Huh Yunjin, Natty, Lee Haein, Bae Eunyoung, and Lee Sian. However, similar to her JYP experience, this debut opportunity ultimately fell through, adding another layer of disappointment to her trainee journey.

Challenges and perseverance

The consecutive setbacks took a significant emotional toll on Mashiro. "After I was unable to debut at JYP, I tried other companies, but I felt like I had no future," she reflected in a later interview. "The trainee period continues to increase and 'Is this right?' I thought so. I had a lot of worries at that time, and my faith in myself was broken".

Consequently, Mashiro made the difficult decision to return to Japan, where she took up part-time work at a BBQ shop. At age 20, she found herself mentally exhausted and contemplating whether to abandon her idol dreams altogether. "I was so exhausted that I even thought, 'I don't have to prepare for being an idol anymore,'" she admitted.

Nevertheless, a pivotal moment occurred when she watched her former co-trainees performing as ITZY members. The sight reignited her passion for performing. "I was very envious," Mashiro confessed, realizing that despite her verbal declarations about giving up, her "heart didn't agree".

Throughout this challenging period, her mother provided crucial emotional support. Rather than simply offering comfort, her mother challenged Mashiro with tough questions: "So? Are you coming back? Are you going to give up?" This approach helped strengthen Mashiro's resolve to continue pursuing her dreams.

After less than a year in Japan, Mashiro returned to Korea with renewed determination. She signed with 143 Entertainment and viewed the Girls Planet 999 competition as her "last chance". This pivotal decision would ultimately lead to her long-awaited debut—though not in the way she might have initially imagined.

Girls Planet 999: The Turning Point

After returning to Korea with renewed determination, Sakamoto Mashiro found her turning point through Mnet's survival show "Girls Planet 999" in 2021. The space-themed program became the platform where her perseverance would finally pay off after years of setbacks.

Mashiro's audition and ranking

In July 2021, Mashiro entered Girls Planet 999 as part of the J-Group (Japanese contestants), quickly establishing herself as a standout participant. Her introduction video garnered 200,000 views, indicating early fan interest in her journey. Throughout the competition, Mashiro maintained impressive rankings, starting with an initial rank of J02 (second among Japanese contestants).

As the competition progressed, her popularity continued to grow. During episode 5, she achieved P5 in the Planet TOP 9 overall ranking, maintaining J03 standing within her national group. By episode 8, she had climbed to P3 in the Planet TOP 9. Remarkably, in episode 11, she secured the top position among all Japanese contestants (J01) while maintaining P3 in the overall rankings.

Mashiro showcased her versatility through multiple performances on the show, including renditions of (G)I-DLE's "DUMDi DUMDi," IZ*ONE's "Fiesta," ITZY's "In the morning," and the original song "U+Me=LOVE" with Team 7 LOVE Minutes. Her former connection to ITZY members as a JYP trainee added an intriguing layer to her story, particularly when she performed their song.

Leadership roles in missions

Throughout the competition, Mashiro consistently demonstrated leadership qualities that would foreshadow her future role in Kep1er. Her diplomatic approach and responsibility during team challenges helped her stand out among the 99 contestants.

In team missions, she exhibited both technical skill and the ability to guide others effectively. Her performances earned recognition from both judges and viewers, advancing her position in the competition. Notably, she participated in the "In the Morning" team, which won the Combination Mission for 3-person teams, securing 90,000 points each.

Mashiro's leadership abilities were officially acknowledged after the show concluded, when she was assigned the position of co-leader of Kep1er, supporting main leader Choi Yujin. This appointment reflected the trust and respect she had earned throughout the competition.

Final placement and debut opportunity

The finale on October 22, 2021, broadcast live, represented the culmination of Mashiro's long journey toward debut. In the interim results released before the finale, her position had dropped to P14 (J03), creating tension about whether she would make the final lineup.

Ultimately, Mashiro secured 8th place with 708,149 points from voters, earning her spot in the nine-member group that would become Kep1er. The moment was particularly emotional because, as she revealed in her winning speech: "This audition was the last chance for me so it was a huge gift for me".

Her heartfelt reaction revealed just how significant this achievement was: "First of all, this was my dream for such a long time. Thanks so much to Planet Guardians. This time around, I didn't think I'd make it. I didn't prepare the speech even". The emotional moment reflected years of perseverance through multiple disappointments at different companies.

The newly formed group Kep1er (pronounced "Kepler") was officially announced during the finale, with Mashiro joining eight other members selected from the original 99 contestants representing Korea, Japan, and China. For Mashiro, securing a position in Kep1er represented not just a debut opportunity, but vindication of her unwavering pursuit of her dreams despite numerous setbacks.

Debut and Rise with Kep1er

After securing her place in the final lineup of Girls Planet 999, Mashiro's long-awaited dream of debuting as a K-pop idol was about to become reality. The newly formed nine-member group Kep1er (pronounced "Kepler") prepared to introduce themselves to the world, with Mashiro finally stepping into the spotlight after years of training.

Official debut date and album

Kep1er was originally scheduled to debut on December 14, 2021, with pre-orders for their first mini-album First Impact beginning on November 29. Unexpectedly, the group's debut was postponed to January 3, 2022, after a staff member tested positive for COVID-19.

On January 3, 2022, Kep1er officially debuted with the release of First Impact, featuring the energetic title track "Wa Da Da". The mini-album included six songs, half of which were familiar to Girls Planet 999 viewers, including "Shine," "Another Dream," and "O.O.O (Over&Over&Over)". Between these tracks, the album showcased "MVSK" and the standout title track "Wa Da Da," which quickly gained popularity.

The debut proved worth the wait as Kep1er achieved immediate commercial success. First Impact sold approximately 400,000 copies and reached number one on South Korea's Gaon Album Chart. Moreover, both the EP and its lead single "Wa Da Da" made international impact by charting on the Billboard Global 200 and World Digital Songs charts respectively.

Role as co-leader

Prior to their debut, Kep1er held their first YouTube live stream on November 18, 2021, where they discussed group roles. During this broadcast, Mashiro was officially assigned as co-leader alongside Choi Yujin, who took the main leadership position. This appointment recognized Mashiro's exceptional leadership qualities demonstrated throughout Girls Planet 999, where she had consistently guided her teams effectively.

As co-leader, Mashiro brought valuable experience and maturity to the group, helping to bridge cultural differences among the multinational members. Her fluency in both Japanese and Korean proved instrumental in group communication and during international promotions.

Notable performances and fan reception

Kep1er's debut resonated strongly with audiences, leading to their first music show win on January 13, 2022—just ten days after debut—when they claimed victory on M Countdown with "Wa Da Da". Their second win followed swiftly on January 14 on Music Bank, setting a record for rapid consecutive wins. By January 20, they secured their third win on M Countdown.

The group's remarkable debut achievements earned them recognition as "New Wave of the Year" at several prestigious ceremonies, including the Asia Artist Awards and Seoul Music Awards. Additionally, according to Forbes, First Impact broke sales records for girl group debuts with over 200,000 units sold in just the first week.

Fans embraced Kep1er enthusiastically, adopting the name "Kep1ians" and the official colors purple, white, and light yellow. "Wa Da Da" became a particular phenomenon on TikTok, used in over 177,000 videos shortly after release. Mashiro's journey from multiple failed debut opportunities to successfully debuting with Kep1er resonated deeply with fans who appreciated her perseverance and dedication.

Life as a Kep1er Member

Throughout her time with Kep1er, Sakamoto Mashiro built a reputation as the group's nurturing presence, offering stability amid their whirlwind schedule. As a co-leader alongside Choi Yujin, she embraced responsibilities beyond performing, often serving as the emotional anchor for her bandmates.

Mashiro's bond with members

The relationships Mashiro formed within Kep1er revealed her supportive nature. Members consistently expressed feeling comfortable around her, praising her ability to maintain composure in challenging situations. In fact, Yujin once remarked that despite being younger, Mashiro felt older because "she takes care of the members well".

Perhaps most notable was her close friendship with Yeseo, affectionately dubbed "YeShiro" by fans. The pair shared living quarters as roommates and developed what many described as a sister-like bond. Their connection became a highlight for supporters, from Yeseo's heartfelt letter during Girls Planet 999 to their joint vlogs.

In difficult moments, Mashiro's emotional intelligence shone through. After a disappointing ranking on Queendom 2, she tearfully expressed concern not for herself but "how she didn't want the members to fall ill and feel hopeless". According to Bahiyyih, Mashiro excelled at conflict resolution, "listening to both sides and suggesting compromises".

Her image and fan nicknames

Fans affectionately nicknamed Mashiro "marshmallow," both for its phonetic similarity to her name and because it reflected her sweet personality. Her most recognized charming point, according to Mashiro herself, was her dimple. Fellow members consistently described her as reliable, calm, and photogenic.

Her GP999 motto—"Charming marshmallow from overseas"—further cemented this image. Within Kep1er, she belonged to the "Unnie Line" (older members), whom the group collectively deemed "the most romantic".

Languages spoken and cultural fluency

Having trained at JYP Entertainment from 2016 to 2018, Mashiro developed exceptional Korean fluency. This linguistic ability proved invaluable in a multinational group featuring Korean, Chinese, and Japanese members.

Beyond Korean and her native Japanese, Mashiro began studying Mandarin during her Kep1er era, as revealed during the group's first VLive broadcast. This dedication to language learning reflected her commitment to connecting with international fans.

Favorite moments during Kep1er era

For Mashiro, debut day ranked as her "happiest moment" with the group. Her performances consistently demonstrated her enthusiasm, particularly her energetic interpretation of ITZY's "MITM" that impressed viewers.

In interviews, Mashiro defined Kep1ian (the fandom name) with a single word: "inspiration". She approached her time with Kep1er mindfully, once stating: "My team will only last for a limited time. I'm not thinking about the future. As long as I'm happy now, that's all that matters. They feel like a family".

Beyond performing, Mashiro enjoyed cooking for her teammates, with member Hikaru particularly appreciating her gratin dishes. These small moments of connection alongside professional milestones created a meaningful chapter in her evolving career.

Departure from Kep1er

In May 2024, a significant announcement changed the trajectory of Mashiro's career when her departure from Kep1er was officially confirmed. The news marked the end of an era for the Japanese idol who had found her long-awaited debut with the group.

Contract expiration and announcement

Ahead of Kep1er's contract expiration, WAKEONE and Swing Entertainment officially announced on May 30, 2024, that seven members would extend their contracts with the group, whereas Mashiro and Yeseo would conclude their activities. This decision came after the nine-member girl group had promoted together since their January 2022 debut through Mnet's survival show "Girls Planet 999".

The original contract for Kep1er had been established as a temporary arrangement set to last for two and a half years. Following what the companies described as "extensive discussion and consensus," the agencies confirmed that Mashiro and fellow member Yeseo would depart after completing scheduled activities.

Both entertainment companies expressed gratitude toward Mashiro and Yeseo for "their dedication and hard work over the past two and a half years as Kep1er" and promised continued support for their future endeavors.

Final concert and farewell

Mashiro's final performance with Kep1er took place during the group's "Kep1going" concert series at K-Arena Yokohama in Japan from July 13-15, 2024. The three-day event attracted approximately 45,000 attendees, demonstrating the group's significant popularity even amid the bittersweet circumstances.

Throughout the farewell concerts, emotions ran high among both members and fans. During the performances, leader Choi Yujin expressed hope that supporters would "continue to support and love us no matter where we are in the future". Other members shared similar sentiments with tears, marking a touching conclusion to their time as a nine-member ensemble.

Making this farewell even more accessible to global fans, the final day's concert was live-streamed online to 20 countries and regions, allowing international supporters to witness this pivotal moment in Mashiro's career.

Fan reactions and support

The announcement of Mashiro's departure initially sparked concern among dedicated Kep1ians. Numerous fans expressed their sadness on social media platforms, with many sharing compilation videos of memorable moments featuring Mashiro throughout her Kep1er journey.

Throughout the final weeks of Mashiro's time with Kep1er, fans noted emotional moments that revealed her attachment to the group. During one K-wave performance, observers spotted Mashiro tearing up, suggesting the departure was emotionally challenging regardless of the professional opportunities ahead.

Ultimately, Mashiro's devoted fanbase rallied behind her next chapter. Their support remained steadfast as she moved toward her new beginning with MADEIN under 143 Entertainment. The announcement that she would join a new girl group alongside former teammate Yeseo provided fans with reassurance that her K-pop journey would continue, albeit under a different banner.

New Beginnings with MADEIN

Following her departure from Kep1er, Sakamoto Mashiro embarked on an exciting new chapter that would once again test her adaptability and showcase her leadership abilities. The Japanese idol's career transition happened swiftly, giving fans little time to wonder about her future plans.

Joining 143 Entertainment

On July 16, 2024, 143 Entertainment officially announced that Mashiro, alongside former Kep1er teammate Yeseo, would re-debut under their management. This news coincided with a significant transformation as the company rebranded their existing girl group LIMELIGHT to MADEIN. On July 29, Mashiro was formally introduced as a member of the newly configured six-member ensemble.

Debut with MADEIN and MADEIN S

MADEIN officially debuted on September 3, 2024, with their first EP titled "Rise" (상승). The group quickly gained attention with singles like "UNO" and "Love, afraid". In fact, the group held their first Japanese fan concert, "Madein Adventure 2024," at the Orix Theater on October 5-6, 2024.

Yet perhaps most intriguing, on July 31, 2025, 143 Entertainment announced the formation of MADEIN's first sub-unit—MADEIN S—consisting exclusively of Japanese members: Mashiro, MiU, Serina, and Nagomi. This unit is scheduled to release their debut album "MADE in BLUE" on August 14, 2025. Ahead of this official launch, MADEIN S will appear at Kansai Collection 2025 Autumn/Winter on August 6 at Kyocera Dome Osaka, with Mashiro and MiU walking the runway.

Mashiro's role as leader

In both configurations, Mashiro serves as the designated leader. This marks a significant achievement, as she noted, "becoming a leader doesn't happen often with foreign members". Her appointment reflects the confidence placed in her abilities by 143 Entertainment, whose CEO even highlighted her as a "vital member" of the company on his personal Instagram.

Musical direction and concept

MADEIN S's concept film showcases the members under dreamy lighting with distinctive Y2K-inspired styling, accompanied by lyrical melodies. This aesthetic direction hints at their musical ambitions, as the company stated that MADEIN S "will showcase a new kind of charm through music driven by a fresh concept and storytelling". Through this endeavor, they aim to create "a new experience that goes beyond simple music", potentially serving as a strategic bridge to expand MADEIN's international presence.

Personality, Hobbies, and Fun Facts

Beyond her professional achievements, Sakamoto Mashiro's personal qualities contribute significantly to her appeal. The multifaceted idol possesses numerous traits that endear her to fans worldwide.

MBTI and personality traits

Mashiro's personality type has evolved throughout her career, initially classified as an INFP who "sticks to their values and is full of kindness". Her profile was later updated to ISFP. As an empath, Mashiro considers this characteristic both an advantage and disadvantage. She typically finds it awkward to speak informally to seniors, often reminding teammates like Yeseo to use honorifics with her.

Hobbies and favorite things

Among her favorite activities, Mashiro enjoys playing with her cat, taking walks, and uniquely lists "staying still without doing and thinking anything" as one of her specialties. Her favorite colors are purple and blue, plus she appreciates ring beads, bracelets, and pillows. Winter stands as her preferred season, alongside a fondness for good walking weather.

Food preferences and dislikes

In terms of cuisine, Mashiro gravitates toward omelets, fish cutlets, and sandwiches as her favorite foods. She appreciates mint chocolate and fried chicken yet turns away from sea urchin roe, acorn, and jelly salad coriandrum. For comfort food when stressed, she reaches for waffles. Her pizza preferences include both Margherita and Gorgonzola varieties.

Nicknames and charming points

Fans affectionately refer to Mashiro by several nicknames including "Shiro," "Mashmallow," "Siro," and "Siroguri". Within Kep1er, she earned the title "Chef" as the group's best cook. Interestingly, her Chinese nickname became "500" because her name's kanji pronunciation resembles this number in Mandarin. Regarding her most appealing feature, Mashiro herself identifies her dimple as her charming point.