Yoruko thinks that the murder her brother committed seven years ago is a secret to only between them. But the sudden appearance of the victim's hairpin as a present during Ryuuichirou's birthday party makes Yoruko wonder if somebody else knows about their dark secret. 356s5z
3 Volumes (Complete)

The first two chapters have a confusing start. Lots of new names, allusions to various events in the past, and indirect descriptions of family circumstances. The bottom line is that Yoruko's brother drowned a girl named Raika who seems to have deserved it, and now Yoruko is paranoid that an unknown party has sent a message to the effect of "I know you did it". And right then, a ghost shows up for some unknown reason.
After that, the story transitioned to an arc. With the introductions done, I just focused on the practical facts of the story and tried to enjoy events. And I didn't have any problem following them. The pacing is enjoyable and I found the art style cute and expressive. You'd be unlikely to guess who amusingly calls the anti-social heterochromatic Yoruko "chuunibyou". On top of that, the climax of the arc was very exciting and dramatic. The story's moving into another arc now, yet it's maintaining the intensity.
My complaint is that I can't seem to understand the meaning of a lot of lines... Even though the grammar and spelling are essentially perfect. Also, this series comes out every other month, so it'll probably be years before it finishes.