The centerpiece of the anime, the shinrabanshou, is supposed to be some sort of superpower that, I suppose, can do anything. However there's very little detail given about the nature of its use. The consequences of activating it are never really discussed so it remains unclear why Tobari Sensei is so determined never to let it be used, even for good. When he argues about this with Miharu he just repeats himself without explaining his decision. Tobari Sensei had the potential to be a cool "seems like a slacker but is really competent" character, but instead ended up as "guy who has unclear motives that are necessary for plot device" character.
Furthermore, Kouichi's immortality and fighting skills were too inconsistent. At random times he would become an immortal deadly assassin, but most of the time he would just be a kid who was no better than the average ninja and forgot he was immortal. Also he should have immense knowledge if he's been around forever; shouldn't he be conspicuously smart for a high schooler? Needless to say, his character lacked much needed development. There were times when attempts were made, like when he killed all those dudes, but the weren't followed up on.
Miharu and Yoite's relationship made very little sense. It would have made sense if it was intentioned to be homoerotic love but I just don't think it was. Miharu was attracted to Yoite because they were both lonely, but the fact that they remained rather passive and rather undeveloped throughout the series made it difficult to justify caring about their relationship.
Like many plot-centric anime with a rather stupid, one-dimensional plot, the series got more boring and repetitive at the end. At the first half of the show, all the characters are being introduced and developed so the series catches your interest. But by the last 5 episodes or so everyone just starts repeating themselves and reiterating their motives, while the plot unfolds predictably. It's quite frustrating when most character's reasons for doing things don't extend beyond "because I think I'm right" and "because I want to". Those aren't reasons themselves. Those need reasons.
The best character in the series was Yukimi, who had a likeable "tough guy who cares" personality. Even so he did some frustrating things and his development left some things to be desired.
There was an unfortunate paucity of good fighting scenes. The best action scene was when kouichi was beating up the guy with the gun, and that isn't saying much.
On aspect that I was (relatively) impressed with was that they gave the main villain understandable reasons behind his motives. I could at least understand how his intentions could be construed as something for the greater good.
