Mysterious kimono girl. Who is she?

I'm nearly 10 hours in the visual novel so far and we still haven't seen the last heroine appear which is puzzling. Her only scene is a flashback of Akito's past (she was wearing a kimono) in relation to the trauma that caused him to leave the magic show scene, but the details are fragmented at this point. My bet remains on the little sister route as the visual novel lacks one otherwise, but we don't even have a name at this point so it's hard to guess.

The rest of the progress has mostly been on knowing more of the heroines personalities and quirks. For example Clarice is scared of males which is part of the reason why she has trouble in excelling in her dancing passion. I like quite a lot how she interact with the protagonist and how she's slowly opening up to him even though he's a male. Among the heroines she's the second in my ranking after Karentia.

Sofia instead continues to trail behind, she's a deredere heroine which I usually like a lot, but the shy/indecisive attitude and her inability to talk properly somehow irritates me a bit. Hopefully she'll grow as she goes over her low self-esteem problems, the design is solid so just need a bit of a push. On the positive side, she already found a good friend in Monica, the scene with the two talking about anime or other otaku things together was quite cute.