after the monsters got to the surface half of the humans didn’t want the monsters to be free and said that they deserved to be cast down again. And so another war started and this includes your undertale oc, Gerson, Mettaton, Asgore, Undyne, and some other members of the royal guard and monster kind fight in the battle as Gerson is too old to fight with his hammer as his vision is getting blurry with each strike the humans make as he is leaning on his hammer while his legs buckle beneath him