Shinobu Tsuji is the 18 year old sister of Ryuu Tsuji.
Shinobu makes a brief cameo in chapter 65 of the SA series. She makes her actual appearance in an SA fanfict. She loves Ryuu very much and cares for him. She loves him so deeply that she has a room filled with pictures of him throughout the series. She was also able to say that Ryuu was growing apart from the Yamamoto Twins and was instead growing closer to Finn.