Tokyo Ghoul, Jujutsu Kaisen (TV) Recommendations
In both, the protagonist deals with an unknown demonic being inside his body. And constantly (based on the OP) decides a dilemma if he's a good or bad guy after all.
Both are dark urban fantasy in which the protagonist becomes a monster of some sort and must adapt to these new conditions. They share a very similar horror atmosphere and aesthetics. Both have gorgeous sound and visuals.
When it comes to darkness, both Anime have the same vibe going on. Malicious enemies with gruesome monsters, Tokyo Ghoul and Jujutsu Kaisen are in the same boat. They both have demons and monsters in them.
And OH LORD! That action is crazy. Tokyo Ghoul has phenomenal action, and fighting scenes are out of the world.