[Fujikira]

Spoiler for Shmion:

1.This is Shion since it's mainly her introduction towards the entire series.
2.That is Mion she wanted to get close to Keiichi to, be recognized as a girl from him, and by disguising herself as her sister whom Keiichi thought of as more womanly.
3.I'm unsure on this one
4.Again this is Mion, since she was more involved in the dam project while Shion was still in her school in the whilst of it
5.At first it's Shion, but the next day when Keiichi devises a plan to help her it's Mion.
6.It's actually Mion, the twins devised a plan since Shion wanted to help Mion to be recognized as girl to Keiichi due to him giving the doll to Rena that resulted into Mion becoming upset, and from when she told Shion about it that's when they decided to switch around with Keiichi.
7.That is Shion, in chapter 6 it's revealed that Shion asks Keiichi again at a fountain disguised as Mion to cover up her tracks.