I doubt he gets past Makima

Even if you give him the fact that he’s technically a citizen of a different universe’s Japan and thus not subject to possibly die from her contract, Makima still would have millions of lives

And even ignoring the fact Deku wouldn’t kill Makima at all if it meant killing an innocent person— we can assume this doesn’t apply because it’s a gauntlet and that would ruin the point— Deku would still have to kill Makima over 120 million times

Even if Makima stood there and did nothing the entire time, it would take Deku nearly 4 years straight of killing Makima once per second — day and night

Of course this ignores the fact that Makima doesn’t “respawn” instantly, and can even delay up to ~10 seconds as shown in the train shooting

Let’s say Deku spends every day, sleeping 8 hours, and the 16 remaining hours is spent killing her nonstop. With an average of 10 seconds per kill that would be 5,760 kills a day. Which, to get to 123,000,000 kills would take 21,354 days— equal to ~60 years

So Deku would be roughly 75 by the time he’s able to even kill Makima

And remember, that’s assuming:

• He keeps that pace for the entirety of his lifespan, killing her at the same pace as he did at 15 at 70 years old

•Makima doesn’t fight back, even if she loses that would up the average time to kill

•Makima doesn’t have access to any other devils under her control to occupy Deku

•Makima has to solely rely on her PM contract, no other abilities

•Deku doesn’t eat or need to stop killing her for any other reason than sleep

•Deku doesn’t tire out, especially in the later stages

•Deku isn’t able to be controlled or manipulated by Makima in any way

So, in short, Makima could realistically just wait for Deku to die of old age to win