X-Tale is the main comic of the X-Tale universe by Jakei95, and the precursor of Underverse. The story takes place in Timeline #10, where everything seems to be going normally, until X-Tale!Sans starts having some memories of his genocide run, a direct fault of X-Event!Frisk. This would lead to a series of events that would finally bring an end to the universe.
Years after X-Tale!Frisk shattered the barrier, X-Tale!Sans and X-Tale!Papyrus are both heading towards town hall, in which X-Tale!Undyne surprises the both out of nowhere and takes Frisk. This turned out to be a test, however Sans was acting much stranger than he ever was, especially when he tried to killed X-Tale!Frisk.
After the two are taken home by XGaster, he determines if he should overwrite or not. Meanwhile, Sans begins dreaming of X-Event!Chara, and he feels as if his soul was slowly being corrupted.
While at a ceremony to promote peace, Sans nearly kills X-Tale!Frisk had not XGaster intervened. He flees, only to be caught by X-Tale!Mettaton. Before he could explain to his brother, the time resets again, this time with the ceremony going on normally.
As it turns out, both X-Event!Frisk (under the influence of X-Event!Chara) and XGaster are both fighting against each other for control of the timeline, and that this timeline was rewritten 10 times thanks to the power of overwriting. Despite showing Sans the motivation to kill them, Sans' refusal leads to a battle which ends up getting Sans his signature scar, and the name "Cross".
XGaster resets the timeline, but Cross still has his scar from the battle earlier. As both him and Papyrus head out to town hall with X-Event!Frisk, X-Tale!Undyne tells Cross that he's no longer needed, and as he struggles against the battle that is going against him, XGaster is getting his treatment with everyone from X-Tale except Alphys. As he's dying, he reminds the X-Event that they'll never find his other half and that he'll always be watching them failing to get it in vain.
Realizing his refusal, X-Event!Frisk goes back to attack XGaster, but his plan is halted after Cross enters in, using blue magic on nearly everyone except Papyrus and eventually kill them and his brother. At the mean time, XGaster asks X-Tale!Alphys to store all of his entries, seeing that his death kills the universe. With the majority of the main cast dead, Cross proceeds to absorb the powers of the X-Event, which he does by taking the soul of X-Event. However, his status as a monster, and X-Tale!Frisk's death from him, meant the universe was dead on arrival and he is unable to overwrite at all. That is, until he came.
The main protagonist, X-Tale!Sans/Cross is unassured after he begins having problems related to his code (e.g. He wants to kill X-Tale!Frisk). His actions have placed him as a tragic hero, being his own fault for his universe's failure to exist.
X-Event!Frisk is the main antagonist of the series, along with X-Event!Chara. The two of them keep messing around with X-Tale!Sans's own coding to try to kill themselves (possibly to free X-Event!Chara), and once that fails, he begins rallying up support against XGaster with the rest of the cast. He fails to, however, kill Cross, and this results in him being killed after Cross takes their soul, during a heated confronted between his brother and Cross.
X-Event!Chara is X-Event!Frisk's other half of the X-Event pair, expressing his interest into disposing XGaster as well. He plays no specific role until the near end of the comic, at which he expresses his disbelief that his brother is gone, and repeatedly attack Cross for what he did.
XGaster is the creator of X-Tale, and the tritagonist of the series. Though he's equipped with his overwrite ability, he's unable to use it thanks to his soul's lack of power, allowing his kids to use it at will. It is revealed soon afterwards that he hid the soul somewhere else to prevent them from taking it, and after he's ejected by Cross to fight the cast, he's completely wiped from his universe, expressing interest to see what his X-Event can do.