She suspects her best friend, Itsuki, of harboring a secret crush on her boyfriend (Nachi), and is intensely jealous to the point of arguing with Itsuki. Itsuki is absolutely furious, because Itsuki has always liked Mike (since the first few chapters, even), who just didn't notice it (well, not really Mike's fault though). And then Itsuki just forgives her. In one chapter.

Oddly enough, despite the Itsuki-Mike thing, this series doesn't really qualify as shoujo-ai. Itsuki's issue basically takes a backseat to Mike's issues every time and there is never any interaction on that level. Nor does Mike ever, ever, ever notice.

Near the end, Mike selfishly asks Nachi not to drop out of school to follow his dream, just so she can do stuff like go on the school trip and have festivals with him. She already has a key to his apartment but immediately jumps to the conclusion that she won't be able to see him. So he gives up quitting school for her. Then, when she finds out he won an award and said that he'd become a pro, she immediately feels betrayed, even BEFORE he decides to go back on the promise. She feels like she's restricting his freedom yet continually looks weepy and unhappy even after she's appeared to have decided to let him go. Obviously he's going to feel bad.

Mike is the kind of girl who should be broken up with, because she's the kind which is so paranoid that she takes everything as a portent of breaking up. ARRRGHH!!

she helps Itsuki, Nachi, Nachi's brother, a Nachi stalker, and a stabber get over their long-time emotional issues, basically by being selfish, irritatingly nosy (that's not just my opinion, everyone said she was irritating), or getting them into bad/dangerous situations.