Synopsis: I wanted to tell a story in a game world but I didn't want to actually build the world.

The Issue: The story is a gamer world story with levels and skills set in the modern world. Dungeons appear in the real world and now people go dungeon crawling with medieval weapons and armor. There is magic or the tablet ht MC gets would not work or have the "gamer" effect it has on him. We see that Japan still has a modern military as they show up to the MC's house when the dungeon is discovered. We know they still have gas and electricity as we see working card and the MC using a computer. We know there is an internet as we see the MC using it said computer. Yet people go dungeon diving using gear from the middle ages.

The best lame excuse I heard for this is that Japan does not have a lot of guns.

Why this is an issue: It is a plot hole that kills the suspension of disbelief. AS a manga/Anime fan going on 30yrs I can accept a lot of Manga/Anime logic. This is not one of them as it is nothing more than the author being lazy.

"Suspension of disbelief, sometimes called willing suspension of disbelief, is an intentional avoidance of critical thinking or logic in examining something surreal, such as a work of speculative fiction, in order to believe it for the sake of enjoyment." - https://en.wikipedia.org/wiki/Suspension_of_disbelief