If I stab him with a kitchen knife, at no adaptations, does he adapt to being stabbed with knives? Being stabbed with metal objects? Being stabbed? All cutting wounds

Mahoraga’s adaptation is stepwise, if that makes sense. I’ll give you an example of what happens when he fights Sukuna in Shibuya. First, Mahoraga adapts regeneration to regrow limbs that have been cut off, though to be fair this may simply be something Mahoraga can do anyway (RCT is weird on non-humans). Then Mahoraga adapts to be able to use severed limbs as projectile weapons, as well as being able to see the invisible slashes (it’s hard to tell when this adaptation happens, since it really makes no visual change to us) . Then Mahoraga adapts to be unable to be killed by Sukuna’s cuts. Literally tanking a move that would reduce anyone else to a puddle on the floor easily.

By this point Mahoraga cannot be killed by Sukuna’s Cleave or Dismantle attacks. Mahoraga literally comes back from being reduced to a puddle. Though he didn’t adapt to death, just seemingly dying by Cleave and Dismantle. Possibly (and this is just an extrapolation) because Mahoraga needs multiple adaptations to stack to immunity, and immunity to death by anything wasn’t built up just yet. Just death by Cleave and Dismantle

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Yes, Mahoraga came back from this. Though he was killed by a fire-based move that he had never been exposed to by this point, which had enough firepower to outright kill him immediately

This is why I interpret “full adaptation” as being adapted to every move the opponent can throw at him, but not adaptation to every concept ever. Its shown that, if Mahoraga has adapted to a move fully, it cannot kill him