"That" is a being that traverses countless otherworlds, saves and guides (and destroys?) them.

"It" has visited countless otherworlds, saving, guiding, and destroying many people there. "It" has prioritized those around it above all else, repeatedly captivating and saddening others. "It" has prioritized itself above all else, pressing forward on its own path without caring about those around it. "It" has acted according to its own desires, transforming the world into both hope and despair. "It" is, "It" is, "It" is, "It" is, "It" is, "It" is "It" is "It" is "It" is "It" is "It" "It" "It" "It" "It" "It" "It" "It" "It" "It" "It" "It" "It" "It" "It" "It" "It" "It" "It" "It"… Suzuki Kotaro is an utterly ordinary (?) high school boy found anywhere. Today, just like always, he heads to school with his familiar companion Akai Reina, and is supposed to spend another ordinary school day as usual, but... An extraordinarily beautiful transfer student!? The entire class is transported to another world!?? His abilities are utterly ordinary!??? Just as Kotaro and his classmates are panicking after being suddenly transported to another world, they are told: "Brave heroes of the otherworld! Please, I beg you, defeat the Demon King and save this world!!!" Will they be able to slay the evil Demon King, save the otherworld, and return to their original world!? ...No one knows what "It" is.