Dark Cat

Both horror anime include gross/gruesome features and parasites.  

If you want to experience 2 to 5 minutes of pure concentrated nonsense at the beginning of an OVA, then this one is for you. What follows is a series of bizarre and confusing events with equally questionable dubbing decisions. Of course with so bad it's good anime like these, watching the dub is the way to go for maximum comedy. 

So similar to each other in the eroguro dept. and the thing that possess the human transforming it into something grotesque, also the romance between the two is tragic... 

Both titles are OVAs from a similar time period (late 1980's-early 1990's) that have similar art and animation. The main characters in both Dark Cat and Digital Devil Story Megami Tensei have very similar looking character designs. They both focus around supernatural monsters that are attacking innocent people and it's up to a special high school student to stop these monsters from taking over the world. They both have a similar dark and gritty tone with violence, blood and nudity. If you like one, you will enjoy the other.  

Both are action horror anime with terrible dubs, violence, gore and nudity. Both anime came out in 1991 with similar animation, and a similar dark and gritty tone. Both anime also have similar story themes with evil forces trying to destroy the Earth.