He curbstomp the rest of the hero party easily, then spend a little bit of time exposition about his past.
The short version of his past is that there's this tower where it's basically EX dungeon, with even the 'first floor' of it has lv 92 boss and anyone even trying to attempt it would need to be lv 90+.
Nalgoar? He's actually floor 69 (out of 70)'s Keeper, level 99.
As for why he's doing this mid-boss thing....
Well, dude's just lonely. So he want to be a mid-boss, who'd be surrounded by subordinates.
Then once he's done being moody, he turn to the last figure in the robe and attack it.
At which point these chain come out and grab his hands and binds them.
He then noticed that it's not that the other3 people didn't care about their 4th member, it's that this thing is so divine that the others didn't notice it was next to them all along.
More exposition from one of the supposedly defeated hero party member, who call him 'sempai' and how she'd like him to figure out who she is when she introduce herself/those chains.
But nope, stab.
And after giving that 'welp, see you in 100 years' talk, his consciousness cutoff.
Then we skip to the human body (10 years old) , where he's treated like trash by the gang leader kid in the village because the gang leader got a crush on his childhood friend (who he also have a crush on) and don't like it that she's close to him (like, they've bathed together as a kid close)
So today's ordeal is tossing him into this forest of monsters.
Stuffs happen, including getting both his hands cut off, use the blood to do a 'summon' (his current class is Summoner), and out come one of his hands and the chain on it also broke.
(While he can't use other magics, his hands can, so he just have one of them regenerate back his human hands)
He proceed to....'peacefully' take down Owlbear and Oldboar until they finally stop their hostility.
But the important bit is that he realized the dagger that stabbed him wasn't meant to kill, after all even if it was a backstab surprise attack, as a level 99 boss there's no way he'd die in a single hit like that.
That dagger was another mythical item meant to reincarnate him.
Latest chapter of RAW is Oldboar give him and the childhood friend (who snuck into the forest to try and rescue him and damsel herself) a ride back to the edge of the forest, where upon hearing the adults looking for him, they got down from the Old Boar and go back to the villagers.
Where upon the adults start scolding the MC for sneaking into the forest.
MC was like "wait....seriously? no matter how much of a trashbag he is..." look at the gang leader, trash smug face "well then"
At first the MC was about to do a whatever apology since that'll end this faster.
Then MC felt something and shout for everyone to get down.
All the torches go out. incoming spooky dragon-thing.
Chapter end.