They snuck among the monsters into the Underground during the initial banishment because they were already friends with Asriel and didn't want to be separated. They died via the Royal Scientist of their time, ending up her lunch, right in front of Asriel's salad. They Reset several times and tried to avoid this fate but it happened over and over again no matter what route they tried, so they gave up. In the mayhem their soul escaped to wander the Underground for ??? years.

One fateful, fitful night, Bunny drove his boyfriend to murder him. His panic attracted the wandering human soul who made a deal with him to see if he could avoid his death flag, unlike themselves. He would get the ability to Reset and Remember; they would get to watch. He kept repeating his same mistakes. Eventually he began to do it on purpose. When he finally tried for a Good End, it did not go well.

After Bunny was sent to the void, the Underground was a dusty hellhole courtesy his means of proposing to Fuse--the only survivor. He attempted suicide, but before his soul shattered Splat proposed the same deal to him as they did Bunny. He accepted. The following year, they acclimated to each other's presence and became friends. Then the last human fell and slaughtered their way through the Ruins Orphanage.

It took about eighty-or-so Resets for Fuse, Splat, and eventually Shel (Alphys) to figure out a means to kill Frisk and use their soul to break the Barrier before they could Reset, themselves. This plan consisted of subterfuge, misdirecting the Orphanage staff (Undyne, Papyrus, the old Royal Couple, Moffy), poisoning the Orphanage humans in order to collect and absorb their souls, and even then Splat had to (meta)physically keep Frisk in check until the souls (including their own) were expended on breaking the Barrier and thus used up. They are presumed "dead, but for real," alongside the rest of the human souls involved.

2 lazy for comix but just not too lazy for whatever this is
#UndertaleAU #AUChara #AUAsriel
#AUGaster #AUSans #AUFrisk