Ouken. Especially once you get to learn more about him and who he was. When he appears in the series what's left of him is essentially just an animated, demonic armor; incapable of speech or pretty much anything except rasping laughter, heavy breathing or mad roaring as he gleefully brings bloody carnage to those around him. It's not helped by the fact that no matter how hard he's beaten down and diced up, he keeps coming back again.
His backstory in the OVA series is even more ripe with this, both of the visual and psychological kind; and being aired around the midnight slot on TV, is also appropriately gruesome. Everything from his father violently butchering his own people in pursuit of immortality to Ouken's own slow descent into madness after awakening his, until eventually he sees his father's face in everything and everyone he looks at.
There's Miranjo putting Bosse's frozen corpse in a meat grinder and forcing Daida to drink the mush that's left.
The Gods of the setting all tend to embody this in some way. We have Satun rotting alive and slaughtering people for his own ends, the Smiling God who brings about genocides for fun, the Wish-granting Devils and then the God strolling outside of the Treasury of the Gods looking for people to swallow hole.
