I, Hiro Bouchi, was ostracized by the entire school because I stood up against the student who held an absolute power in the school. But no matter what kind of bullying I received every day, I never yielded. Today as well, I was getting beaten up behind the school building. But at that moment, I heard the students screaming―That was the moment when the world was transformed.
On the school grounds, the students were being attacked and killed one after another by monsters that seemed to have come out from an RPG. Using this opportunity, I managed to escape and return home safely. Then at that time, I realized that I had a strange power dwelling inside me. A skill called "Shop."
As long as I could pay for it, I have the ability to buy variety of items on Earth, and even fantasy items that couldn't possibly exist on Earth. In this world, where humans were gradually being wiped out, I decided to make the most of my new skill to live a slow, comfortable life free of worries.
It was truly thrilling and delightful to see all the people whom hated and ostracized me being killed one after another because they didn't have the power I did. This is the payback story of a boy who was once bullied, and uses his skill to take advantage of those who are now left with nothing.
(Source: Shousetsuka ni Narou, translated)
— Description from AniList community (anilist.co).
