History: Entity 004 was originally a Sans in a genocide route, but in this AU, another soul existed: Pain, this soul can have the power to see different timelines.

While the genocide route happened, Sans have an idea, absorb the souls when Frisk reach the Last Corridor.

The fight happened and since the Pain soul could see timelines where he died, he didn't get hit in any part, after the fight, Sans absorbed Frisk soul.

Sans stopped the human but he wasn't really interested in breaking the barrier, he think that Frisk would reset any time after that.

But since he have all the souls, he could have a crisis named: A.T.R.V(Alternative reality Timeline Reset Vision). And since that he was seeing many AUs at the same time. Most of them genocides

These visions was getting on their mind and since that, he was having more aggressive personality.

One day, his brain focused in only one AU: Insanity. and his determination went more and more, now, every single reference that he have of humans he would instantly kill.

After some time, Sans determination went so high that he could get in another AUs. and his body turned into just one thing.

Every human that he CAN see, he WILL brutally kill it.

ps: this is not an au that i will make its just an fun thing that i thinked in 10 minutes.