In This Life, The Greatest Star In The Universe - Chapter 19:

The spring fountain town of miracle that heals anything, Polka. In the hometown of memories, with my dear parents, there was a figure of a half-elf girl who swore to become my female slave.

Repeating such a memorable talk every time he drinks alcohol, 25 years old Andy Smeyson is a former blacksmith’s apprentice and an innocent crossbow soldier. Andy is surrounded by nice companions and competent and sexy bosses, which is different from what he had thought when he was a child, but this was a cozy life. When the half-elf girl suddenly appeared in front of him, he will jump into a furious destiny. Andy, who is weak but courageous​ and clever will meet a lot of different race ladies such as elves, half elves, dark elves, loli dwarves, dragon girls, beast girls and make them his female slaves one after another. The horny adventure started from a half elf girl who doesn’t stop liking him will eventually become a legend ──.

He loved her. She left him for someone richer.But that night, something awakened in Nishanth — a system with no fame boosts, no fantasy powers, and no second chances.Just money. Assets. Ownership.The Infinity Spend Protocol doesn't make him a hero. It makes him a Spend King — a silent force who crushes rivals, empowers the poor, and stuns the nation with outrageous moves.From the slums of Warangal to the boardrooms of Mumbai, Nishanth spends to dominate — buying failed properties, funding orphan tech labs, and humiliating those who once laughed at him.And when the world finally asks:“Who is behind all this?”He walks on stage and answers,“The boy you forgot. The man who never forgot you.”Spend. Dominate. Rise.This is the rise of India’s Spend King — a man who never needed fame.........Only the fire of betrayal.

Legend says, that there is a great demon, who is the human kind’s public enemy. He is the galaxy federations’ nightmare as he wanted to conquer the whole universe. On the first day, he completely took out the human fleet, plunging them into disorder. On the second day, he declared that he will wipe out the whole federation. On the third day, he declared——that the hero who shot him in their previous battle must marry him, or else, he will destroy everything.

The galaxy federation president and the council members had a long meeting after that. They decided to dispatch a soldier, Wu Xing Yun, and marries him off to the arrogant demon. Wu Xing Yun was once a hero who fought for the nebula, and henceforth, he was tasked—— for the sake human race and the universe’s peace, to eliminate mistresses, settle his matters with the mother-in-law, and fix the man’s crooked ways.

Wu Xing Yun was very perplexed when he asked his commanding officer: “Sir, why did it have to be this way?”

Commanding Officer: “Soldier, bear in mind, that this mission of yours, is for the sake of the universe and mankind’s happiness. You must hold on to your husband, and fight other mistresses! Do you have the confidence to accomplish this task?”

Wu Xing Yun, stood straight, saluted, and instinctively replied: “Sir, yes sir! I will accomplish this task!”

- Description from Novelupdates

Long Fei, a cross-timer and doujin, is an otaku who traveled to another world. In the original world, he was an otaku fan of Gundam and military science fiction.

He died in an accident and was reincarnated into another world. The Gundam works he had read before his death and the techniques in various military novels could be brought to another world.

How would he use the Gundam that Long Fei created? What waves can be caused in this different world?