Baoh the Visitor

A parasite called Baoh lives in Ikuro Hashizawa's brain, put there by a shady organization called Doress that wants to weaponize him, and he comes to on a train with no memory of how he got there. The catch: when he's in danger, the parasite takes over and turns him into something that can tear through pretty much anything. He escapes the train alongside Sumire, a nine-year-old girl with psychic abilities who's also being held captive. Now they're both on the run, and Doress is sending everything they have to bring them back. This is a single OVA from 1989, so it's short and wastes zero time getting to the chaos. The Baoh parasite works almost like a biological armor system: blades from the arms, acid, regeneration, and the action leans into the body horror side of things without apologizing for it. The 80s animation gives it a gritty, dense look that holds up better than you'd expect. If you've seen Parasyte -the maxim- and liked the idea of a human host slowly figuring out what lives inside them, this covers similar ground in about 50 minutes. Fans of Elfen Lied's mix of a dangerous escaped subject and a ruthless pursuing organization will also find familiar DNA here. It's dark, it moves fast, and it doesn't overstay its welcome. sometimes a contained, violent 80s OVA is exactly what you're looking for.