he implanted a magic stone into his body, honestly i also dont remember more than that
He had the ss and L-class dragons magic stones implanted together in his chest to give birth to another dragon
When he beat Diarma’s ass in the mind-realm, he got Diarma’s core as a reward. From what I remember he later cut open his chest and shoved that core inside of himself (to incubate it?), hence the scar. Probably can’t heal it cuz it’s an L-class wound caused by a transcendant’s (Diarma’s) core lol
The heart implant happened from the end of ch.95 to ch 96, if you wanted to reread that
I actually cant remember how he got that scar on his chest can one of yall remind me, please