Invincible Monster Fighting System

It's the end of the world. A young man is reborn 10 years ago and becomes a child. He also has a system that allows him to travel to another world to fight monsters and upgrade? In other words, he is invincible. You said your family is rich? Sorry, I lost more money by killing just two monsters than you did. You said you are a second-generation official? I really can't compare to this, but I can solve it by just throwing in a skill. This article is an invincible cool article. The whole text is written with the same word cool. I declare in advance that there is no harem in this book. This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.