The movie tries to get in a really tough subject matter. While doing so, it does steer away too much though. The constant flashbacks (Rashomon this ain't) and the pace do not work in favor of the movie. The subject is very serious indeed (bullying) and is not to be taken lightly (no matter what country it happens and it unfortunately happens a lot), but while the movie does not take it lightly, it does try too hard. The moral finger pointing is heavy ... too heavy.
The anime style is good throughout, but the movie still felt like it had double the running time. One other thing that made it penetrating and almost unbearable were the subtitles. The filmmaker is (likely) not responsible for those, but it does add to the overall dissatisfaction you might feel while watching this. A feeling that arises because you might feel that this subject matter could've been handled better.