Highschool of the Dead Harem x Male reader

You Y/n Dempsey, the son of Tank Dempsey, you joined your father during the Great War and fought hordes of the undead, with Takeo Masaki, Nikolai Belinski and Dr. Edward Richtofen. After the defeat of the Shadow man, Dr. Monty discovers that his other half has sent an agent of his to an alter reality.
So He sends you to that reality to stop this agent, how will the story play out.