Hi all to start off, here is what i remember. A boy is born with a tattoo on his forehead and it's called the "beast" everytime it takes over he literally becomes like a beast and starts roaring and attacking.... oh and people with those kind of marking are shunned. i believe there was also someone else who was born another tattoo. Though i do not remember what it was called. Edit: found out it's Japanese. But still no name, also just remembered that the tattoo doesn't look like a animal or the sorts. It's along the lines of a tribal like decepticons logo
The Portal of Wonderland ? There is a Desert arc(2nd Volume.) that starts with MC getting poisoned by Snake(?) Tattoo, he got info how to get rid of poison from refuge from destroyed clan that can't really control his transformation. - Probably not what you seek, but better than nothing.