This is a very impressive psychological and mystery seinen manga. It also has a bit (or a lot?) of supernatural and tragedy.
It centers around a struggling mangaka who has the ability to "Rerun." Whenever he comes across some kind of tragedy and he fails to stop it, he enters a "rerun" of the incident and it continues to rerun until he finally solves it in a favorable outcome. The first example of this are of him saving a kid that would have been ran over by a truck driven by someone who had a heartattack and died. Another is of him saving a kid who had fallen down an elevator shaft of an abandoned building.
Eventually, this leads up to him coming across his mother who has been stabbed in the side and is dead. He thinks he sees the culprit, and begins chasing him. Don't want to given spoilers, but this leads to him doing one big massive "Rerun" that sends him back in time to the 80's when he was an elementary school student. This is the time-frame where most of the series seems to take place (At least so far).
The reason for this is because, in his child hood, his town played host to a serial killer who would kill children (only females) and then frame someone else for it, thus getting away with it and moving on to the next victim. It is hinted at, fairly strongly, that the murders that happened in his childhood were related to his mothers death. The series then follows him as he tries to prevent the murders and catch the culprit... which is hard as he's stuck in his childhood body.
Anyways, it's quite interesting. Has a bit of Detective Conan mixed with some more hardcore murder mystery. I usually don't like mystery stories much, so I was surprised by how much I love this manga. It's because the mangaka writes (and draws) so well. The story is, at least in my opinion, as near to perfect as a story can be. The characters are likeable (or non-likeable where it applies), the plot makes sense (past the supernatural element), and it portrays the question most of us have asked ourselves, "What would we do differently if we could go back?"