Invincible to Steel

A hundred years have passed since the Third World War, and another two centuries have passed, and the Fourth World War is about to come. Youyu just wants to be an ordinary soldier, accompany his beloved girl, support his parents, and spend the rest of his life normally after retirement - but the prince comes, the war comes, and the alien beasts from space come too... Destiny has deviated from its original track. How should Youyu go on? There are many cool men in it, and you may be able to find your shadow and ambition among them. But no matter what, Yuyu, he is the protagonist. This is definitely a YY article. As for the extent of it - I will give you an introduction, and you readers can imagine as much as you like.