Regret Arc. By the end of it, everyone will have a version of Kogarashi.
On a side note. Sagiri is almost exploding with that boobs hahaha (Imagine the backpain). I love her design. For the others, they were all normal, Chisaki with shorter hair wasn't as good as the other in my opinion. But wow, Miria really has a good design, but her older high school version is great!