Kyoushoku Soukou Guyver

boy who lives a war between 2 sides 

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. 

Vicious otherworldy armored warriors, warning: 18+Not for young kids these days that are weakhearted! one anime ripped a bit of the other but u can see the simmilarity in it, and this genre was quite wellknown in japan those days! 

Both OVA's are works involved with Toyoo Ashida where he wrote the story for the Guyver OVA and directed Vampire Hunter D. These anime express a dark and mysterious atmosphere where gory violence is quite common. Vampire Hunter D deals with dark fantasy and Guyver: Out of Control covers science fiction, however both are highlights of edgy animation found in the 1980's. 

Both anime where release in the 1980's with similar animation and a similar vibe. The main protagonist in both titles can transform into a powerful armor superhuman being to fight against evil powerful monsters. The main protagonist in both anime also have a similar female love interest that they must protect from evil monsters. They both have plenty of action, violence and blood with a dark and gritty atmosphere. If you like one, you will enjoy the other.