For whatever reason, mysteries and school life go hand-in-hand. All of the natural drama that occurs in school just offers itself to the subterfuge that needs to occur to have a good mystery. There is a natural tension that can be exploited. That being said, it could be simple or an overall rollercoaster, which is what we saw with Arisa by Natsumi Ando.
I think it was until the very end that I did not know what was going on in this story as we follow Tsubasa, who is trying to figure out why her sister, Arisa, tried to commit suicide. The only information she has is that it has something to do with her school, so Tsubasa goes undercover as Arisa. Going in, I thought this was going to be very shoujo-y, given the author, but I would say that anyone who loves manga and mystery will enjoy this. Yes, there are shoujo elements, but they are overwhelmed by the want to get the full story.
This manga talks about self-harm as these are thoughts several characters have had or actually carried out. Take care if you decided to read this.