Stranger's Handbook - Chapter 146: A Trap Called Custom

When the storm struck, they chose Kogan as a sacrifice to save their city... but he found himself in an unknown world, surrounded by strangers who knew nothing of their fate. In a land teeming with enigmatic entities and lurking dangers, Kogan will soon realize that his survival was no miracle, but the beginning of a harrowing trial. Will he find a way to escape, or is this place the grave that was destined for him all along?

When we met for the first time in our first year of high school, he saw my contempt, but silently continued to clean;

After breaking up with his girlfriend, he accidentally acquired a genius system and rose from there against the heavens, becoming invincible..

- 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?

- Description from novelbuddy