To unlock Sumika, you must update Acceleration of SUGURI 2 to v1.3 or higher in order to play Story Mode and unlock her.

Unlockable	How to Unlock
Hime	Play through Arcade Mode as any character from SUGURI (Suguri, Iru, Saki, Kae or Kyoko) without using a continue to unlock Hime.
Star Breaker	Play through Arcade Mode as any character from sora (Sora, Alte, Tsih, Sham or Nath) without using a continue to unlock Star Breaker.
Sumika	Play through Story Mode on Normal or higher with all other characters without using continues.