Kiseijuu: Sei no Kakuritsu, Koutetsujou no Kabaneri Recommendations
Both series involve a glasses-wearing main character being infected by a strange virus/being that threatens to take over their mind. However, in the nick of time, they manage to keep the intruder out of their bloodstream and save their humanity by cutting off their own circulation and blood flow to the brain. As a result, they are now half-bonded with whatever wanted to take over their entire body, giving them a unique set of powers. Both series are packed to the brim with blood, gore, horror, and action elements, set in worlds where humans aren't at the top of the food chain.
MC uses the power of the enemy - "Infected" humans - Enemies become stronger over time
I know that this might seem a bit odd to some but this anime reminded me of Parasyte. The main character sets off to destroy the infected with the virus/parasyte and both main characters in the anime dont allow the virus to spread to their brain. Both animes are about the main protagonist fighting the infected.
Both of these anime revolve around the main character stopping a deadly infection before it reaches their brain, and in doing so end up unlike any species, not human nor infected. These mc's that undertake the change handle their situation with similar approaches, that being to preserve and protect human life despite their obvious condition. Another thing thats similar between these anime is the overall feel, its hard to explain but you just get the same adrenalin rush when you see the mc master their conditions. The only significant difference I can think of is the time these are set, Kiseijuu is very modern whereas
-Classic '90s anime art style
-Protagonist becomes half human half monster
-Well animated blood and gore