He was sent to the future, but then later returned to the past once the conflict was resolved. So now he's in the "current timeline" (which was the time he had left) and he's getting treatment to kill the cells that make him superhuman. It takes 100 days for the cells to completely die off, so that he can finally die a normal death.
oooh that makes sense ty, with him in his uniform when they had the 100 day talk i thought that was in the future, didnt realize that was the current time line
oh wait does he still have power? I thought he just wanted to die
i mean the reason he said was that, during the current + 'past/og' timeline, they found all kinds with the super type cells, like when MC was in hs, so now hes back before the world got gates and stuff but the cells r present. SO he wanted to die to kill them off
like idk the whole bit about 100 days to die again, like i thought he already got the srum and went back to the past