Volume 15 goes deep into who Tsukasa is and what happened to her. It also goes back to the night of the whole car hit and it really works well.

This is probably the most damaged we've seen Tsukasa. Hurt and lost, wondering what her next move is. On the other hand you have Nasa, who's trying his best to remember what exactly happened that night. Leaving us to a pretty satisfyingly climax. I believe we will soon be going back to the past to learn Tsukasa life all those years ago. Hopefully it remains as entertaining as the rest of the series has been.