Kyoushoku Soukou Guyver, Devilman: Tanjou-hen Recommendations
Guyver and Devilman are quite similar in plot and the themes they touch. Both anime feature a main protagonist that gains a special power, which turns them into a killing machine. However, they must fight against powerful monsters, turning into heroes of some sort. Both anime are made around the same period, so they have a similar type of art and animation, plus they are both quite violent.