Last Breath of the Genocide

Many Genocide Routes have past for a very long time, for it has gone for so long, and all known aware by one single monster. But each of it was dealt with in different ways. With one that continues to fight, even when the odds are against him. And another, when he went mad and killed off the rest of his kind. But the outcome of each Genocide...it always ends the same. A mysterious door, it opened, and within it, is someone lost inside of the void, as they aid the ones that had awareness of what was going on, but not to the fullest extent. But what happens...when both of the routes collide together? What happens when the both of them, despite being of opposing alignments, work together to stop the Genocide?

(The version of Last Breath will be based off of the one from Fantasy Violin, and the Last Genocide will have both his usual powers and the powers of his Fanon FDY Self, meaning he has all the powers of the main monsters he's killed. I'll even use some elements of Revolver Animation's Last Breath vs Last Genocide animations)