The Truce was the precursor comic to both X-Tale and Underverse. It told the backstory of Error!Sans's and Ink!Sans's backstory as rivals, as the two end up on a mysterious island they can't escape from. The comic was the first to be finished that is related to the X-Tale universe. However, the comic was later revealed to no longer be considered part of the X-Tale/Underverse storyline.
While arguing over the multiverse, Error and Ink are both taken to a mysterious place where they can't use their attack anymore. As the two of them panic over what to do, they're both taken into their own world by a mysterious voice, who tells them that the war is over.
After returning, the two finally decide to be "friends", which allowed them to leave. They both decided on a truce: If Ink promises not to make any more AUs, Error could not delete the others. Despite this, Error still had a distrust of Ink, and would give Ink the impression that things are wrong.
Later, Ink finds out that another AU was deleting itself and comes to save it. It turns out to be a monochromatic world called X-Tale, with the only inhabitants being X-Tale!Frisk, X-Tale!Chara, and XGaster. After showing XGaster the multiverse, he's convinced to create his own game using him and his children.