Kreig was summoned to the other world 130 years ago, the last 30 of which were spent in a constant, vengeful war against any army that would attempt to subjugate him. Once he returned, he found out that only 10 years had passed.

He was given the title of War of the North but he never even knew about it. After all, nobody could get close enough to tell it to him. 

But that all changes one day when a portal opens, allowing Kreig and a small band of soldiers to enter one of many portals that leads to Earth. As it turns out these portals have been opening ever since he was summoned, giving the people of Earth abilities that the world he was summoned to only used to have. But now... now, he has returned. Longing for his former life of peace and understanding, he allows authorities to capture him on the spot, only to be faced with deeply personal questions, such as "who are you?" "what have you been doing for the past 10 years?" and "why is your level so high?"

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...Have you ever read a story where the main guy who got isekai'd returns to Earth. Say, for example, FFF-class trashhero or the necromancer of Seoul station? Say, what if the authorities actually became aware what kind of monster had returned to Earth?

What if they actually tried to use them for something?

Kreig's been in the other world for 130 years, has experienced three great wars, and he isn't okay. Mentally speaking, that is. He's been imprisoned, gained and lost comrades, been betrayed... The whole lot. By now, all he wants is to put it all behind him, something the world doesn't seem to want to let him. 

(Irregular updates, mostly written for fun, no strong planning)