Devilman: Tanjou-hen, Zetman Recommendations
In both Devilman and Zetman, the main protagonist can transform into a superhuman monster and are trying to keep their humanity intact. The main protagonist in both anime battles various monsters that can disguise themselves as humans that threatens humanity. Both are action-packed anime with lots of blood and gore. They also have a similar dark and gritty atmosphere. If you like one, you will enjoy the other.