manga title?

i remember finding a video that covered this manga, but i can't find it either. telling the name of the vid title or the actual manga will work for me

ok so this guy transmigrates or reincarnates into this black haired villain? (i don't remember if he was originally a villain or just a side character) at first he stays low, focusing on his own stats and doesn't get along with the rest of his classmates that much until he saves this lighter haired guy, the original protagonist, who got drugged and almost kidnapped by a fellow female classmate. that guy later commented on he always wanted to talk to mc so he's glad they finally can now. it's shown that the og protagonist is really charismatic and gets along well w/ their classmates, doing so by being able to appraise their powers because he could tell them their strengths and what they should improve themselves own. he and mc later get to be strong friends as adults until they fight in a war(?) or some kind of battle. unsure abt this, but i think the og protagonist takes on a hit for mc or has been fighting for too long, so he's dying. i don't remember it exactly, but the mc then says the lines of smth like "i refuse to fight in a world without you" (a lot of comments joked about how they seemed gay) mc then proceeds to regress w/ the intention to get the light haired guy alive this time but fails and tries again, only to keep regressing.

i don't remember the rest since i didn't finish watching it all