When Two Souls Meet

In this story, it is after the great erase, and there is nothing but a dead au for the X-Event. But one entity still remains, and as a lone adventurer enters that of which can't be escaped, what will they do?

[Important!: I am aware of the true X-Event crisis, how Frisk and Chara had used Sans as a weapon against the rest of the au, but using that couod be suggestively... Plagiarism. So my version of the X-Event is where Error had wiped the existence of the whole au, but two half souls failed to be erased, leaving them alone forever. With Ink's visits, X Sans was able to leave, leave Xin in her own debut. Her own spotlight..]