Parallels
In Underverse, Undertale Toriel rejects her Xtale counterpart's offer of eternal peace. Undertale Toriel tells her counterpart that "Sorrow and Joy coexist", but this has not always been true of Xtale, has it? If XGaster had let the first timeline last, all of Xtale would have had eternal peace. It is what they deserved.
In fact, any story could be joyful and pleasant forever, if not for the intercession of the creator. Despite this being true, Undertale Toriel has not realized it, because her creator has not created an avatar that pronounces changes made to reality, the instituting of death. In fact, this is true of most AUs. The only one that I can think of, in which there are creators, clear-facedly deliver pronouncements about their changes to the world is Reapertale.
This is not because Reapertale's creator speaks directly to their characters. In fact, I am leaving out any direct, out-of-universe creator speaking to their in-universe creations, because that is a minefield when it comes to canonicity and the nature of the world. No, in Reapertale, the characters of Undertale are gods. Undyne is the god of war, Alphys, god of knowledge, Gerson god of wisdom, Asriel, former god of hope, Asgore is the god of the sky, king of the gods, Gaster the god of magic and his twin sons, gods of death. Papyrus delivers the peaceful dead, Sans those that struggle to cling onto life. The AU is named for Sans. What isn't.
Death did not exist in Reapertale, until Asgore and Gerson and Gaster decided that it should be, and so he made them of two black holes. The gods would tell you that it was right, all except for the goddess of Life, Toriel, who loves her children too much. The gods would tell you that the humans fell to apathy and depression, and that death was created to give them meaning. But gods are not meant to die.
The gods cut themselves apart from mortals, when they created death, and so the humans turned upon the closest worshipper of the gods. Nevermind that Chara was treasured by life, that Asriel could not stand death, someone had to pay. And they killed Chara.
Murder was not in the god's plan. Which is why Sans(Reaper) hesitated to strike Chara dead, and why Chara is the Anomaly now. They taught Sans to strike true, but they are not dead. They are the most precious acolyte, turned against the gods by their cruelty, and they cannot die. They exist now, only to spread chaos and destruction. They are a sin that cannot be forgiven.
No one died in the first timeline of Xtale. It took XGaster time to convince himself that it was right. Sans was killed first, and then Asgore.
There was no reason for death to be natural, in Xtale, other than the creators whim. No one is guaranteed to stay dead. But death was what sent Xtale into eternal suffering, under the hands of a mad creator.
There are parallels here. Death being foisted upon a world that did not have it, the betrayal of trust such a thing is, the ways people get back at it.
What I am saying is- the X!Event would not like Reaper very much. They are too much like Reapertale Chara. Especially Frisk.
Frisk kept feeling, you see. Kept suffering. Chara was the victim of Frisk and XGaster first, but Frisk buckled under the weight of death, and then was killed by their brother, and kept their feelings. They cared about death, until their soul was cut apart, and they had to get a backup. Sans may have been the first to die, but he never had the time to process that, and Chara is too unfeeling. X!Frisk and Reapertale Chara are mirrors which reflect the sharp edges of the world around them.
