So in BAAfter, after being killed by Player, two times, instead of being stuck at the save screen in AfterTale, BAAfter Sans soul was stuck at the into a gameplay of Blue Archive before he had to waited for mesmerizing something to begin with.

And then, the new world was created, it also mesmerized a new Sans.

This New Sans was just sometimes remembered that the Old Sans stuck from the previous timeline, who is causing those erasures.

This Old Sans just want to go back to the way he started before he could see his own students again.