Not every Takashi Miike film is a celebration of weirdness and originality. Waru (a manga adaptation) is one of his more inconspicuous features. It has the feel of a filler project, something Miike made in between more prestigious films. It's not a total fluke, fans are sure to recognize some flashes of Miike's talent, but it's probably best to keep your expectations low for this one.
Yoji, a lower ranking member of a Yakuza family, ends up in prison after picking a fight with another gang. There he becomes good friends with one of his fellow inmates, but when his newfound friend is released from prisons he quickly returns to his former life of crime. By the time Yoji regains his freedom, his friend is already dead and buried. Of course, Yoji won't rest until he gets his revenge.
Waru has a pretty basic setup and Miike isn't too bothered with giving the film some extra appeal. Aikawa's performance is on point, there are a couple of inspired moments and the pacing is perfect, but overall it's a pretty generic genre flick that sticks to conventions and tries to go from A to Z as smoothly and effortlessly as possible. Solid filler in other words.