Completion-chuu, Fantasy-ka shita Gendai wo Yuku.

One day, the world has become filled with monsters like those in video games. Though salaryman Hidekazu Satou is astonished by the situation, he feels something burning inside himself. He wants to register all the monsters using the "Monster-dex" skill he has acquired... That's right, he's a "completionist..."

(Source: Kadokawa, translated)