Kyoushoku Soukou Guyver (2005), Devilman: Crybaby Recommendations
Both are modern anime adaptions of classic manga. In both anime, the main protagonist can transform into a powerful humanoid being and must use their new superhuman abilities to protect humanity from monsters that can morph into humans. Both anime are quite action-packed, with a lot of violence, blood, and gore. If you like one, you should enjoy the other.
These two anime are remakes of classic ultra violent superheroes and adapted them into the modern world. Both of these two anime have a human boy transforming into a monster and must fight for their humanity. They both have crazy and violent action sequences while exploring the dark side of human nature.