Everything was caused by countless genocide incidents, Sans tried to stop with all his might but the boy came back and greeted him upon his death. Sans suffered until 998… 999… 1000 But the 1000th time that the dimension or universe he was in had vanished, the gaster who had watched that event saw the door open and rushed out to save Sans and that man because it was the only way to save him. May everyone in this universe come back.