(I do not own Undertale or the picture, they belong to their respectful owners.)
In this AU, Error never left the Anti-Void. Error never remembered his past or anything before living in the Anti-Void. Only knowing he was a error, what The Voices told him, and how to talk and sleep. He never met Ink, never had the need to destroy worlds. All Error had was the Voices. Nothing but screams of how worthless he was and whispering of how he should give up. In this AU, Error never became the Destroyer of Worlds. All he wanted was to stop feeling so lonely, to understand and belong. Error wanted to leave the Anti-Void.
But Balance is needed. Error never became the Destroyer, so someone else would have to.
In this AU, Fresh is more vicious, more violent. He can feel anger, hatred, and jealousy. Fresh became jealous of all the other Monster's being able to feel happiness, being able to feel love. To be loved. He wanted feel that, but couldn't no matter how he tried. In this AU, Fresh became the Corrupter of Worlds. Spreading his fresh virus across the Multiverse, possessing whoever he wanted, and turning worlds into a fresh paradise. All he wanted was to feel happiness and love, to love and be loved in return. To stop feeling so empty.
In one world, their romance would have many hardships, but still stay nothing but sweet.
In this AU, their romance becomes twisted, unhealthy, and dependent.
In this AU, the Multiverse will tremble before them.