Nijika Ijichi's older sister. When they were both young they didn't particularly get along. However, due to their mother's passing and their father's business travels, Seika and Nijika's bond grew stronger and they became close.
She is the owner & manager of the live house STARRY - and her family home is in the apartment above.
Seika lacks practical skills and, due to STARRY, usually has an incredibly busy schedule. As such, her sister performs most of the chores around their home (cooking/cleaning etc).
Described by Nijika as a "tsun-tsun-tsun-tsun-tsun-tsun-tsun-tsun-tsun-tsun-dere" for her, seemingly cold, tough love approach when it comes to both kessoku band and her sister. Even though it is clear that she cares for both deep down, her efforts to portray this could be considered tactless. (Ex. Seika left a concert spot open for kessuko band even after claiming they weren't good enough).
She was previously the lead guitarist in a band. She states her reason for quitting was due to disinterest. Nijika stipulates that Seika opened STARRY for her as she used to bring her sister along to concerts when she was younger (due to the lack of parental presence), these are some of Nijika's fondest memories. Seika would never admit this to anyone.
She was Kikuri Hyori's senpai and friend during college and inspired the latter's interest in rock music. Whilst always apprehensive of Kikuri, even going as far as to reprimand her (along with Ryo) for borrowing money and not repaying in an acceptable amount of time, Seika clearly cares for her - allowing her to use their shower and crash at their place if Kikuri needs to. She also shares distain for Kikuri's drinking habit.
