Seino made her television acting debut in 2011 as Momoka Kurakano in the
Tokyo Broadcasting System Television adaptation of
Bisco Hatori's manga series
Ouran High School Host Club. While
Variety's Dennis Harvey described Sunmi as "a secretive stranger" who becomes "an unstoppable killing machine when ill treated," A second supporting action role, as Mari in the
Shusuke Kaneko film
Danger Dolls, followed. Later in 2014 Seino turned 20 years old while playing the supporting role of Kanna Seki in the
Fuji TV drama
Time Taxi. The next year Seino played the lead role of Ai in
Mamoru Oshii's bullying revenge film
Nowhere Girl, as well as supporting roles in the
TV Tokyo drama
Love Theory, the
TBS adaptation of the manga series
Dr. Storks, the
TBS police drama
Ouroboros, and the
Yoshihiro Nishimura historical film
The Ninja War of Torakage. In 2016 she played the lead role in the short
4DX horror film
Rain Woman and the supporting role of Jaku in
Kankurō Kudō's afterlife comedy
Too Young To Die!. Seino landed her first lead role in a television series as
Tetsuko Kuroyanagi in
Totto-Chan!, the 2017
TV Asahi adaptation of Kuroyanagi's autobiographical memoir
Totto-Chan: The Little Girl at the Window. That same year she starred in the film
Perfect Revolution as Mitsu, a mentally ill prostitute who falls in love with a man who has
cerebral palsy. In 2018 Seino appeared as Yuko Komiya in several episodes of the 98th
NHK asadora Half Blue Sky, and as Riko Akasaka in
NTV's adaptation of the
Hiroyuki Nishimori manga series ''
From Today, It's My Turn!!'' ==Personal life==