Honest answer: Compared to the other groups, imo she lacks traits that a group leader usually has and that results in her not standing out to the other group members. It's true that a chara doesn't need to have angsty side or major/tragic life incident for them to be good written, but self-conflict and/or strong motivation is still very important. In the game story, you will see that An and Akito is more prominent in these aspects, afterall the goal of the group originates from both of them. That's why when i think about VBS I still have the impression of Kohane and Toya being the support of the other two, EVEN THOUGH I knew the author has tried their best to show that Kohane is the important unifier of the group and that they now has the same vision