This whole time I believed Reigen DID get sliced, but Mob’s powers ended up healing him simultaneously. Did he not get sliced?? It was just his suit??
Its just ambiguous enough that you can headcanon as you wish.
It’s possible there was no slice. It is also possible that there was a slice, but Mob’s powers immediately patched it back up, along with his first shirt (mob did put back a good chunk of black vin high school, afterall)