complete at ch32- one of those messed up dark revenge stories with lots of death, but MC is fairly decent despite that, he only kills monsters, his classmates who betrayed him and people who wanted to kill him first.
MC and classmates transmigrates, but he has useless stats and no class but because of this has 10 empty slots of abilities, he is betrayed by his childhood friend + bully to sacrifice himself to the dungeon, he manages to survive in dungeon, exits temporarily and meets another female transmigrator, while doing quest to rank up, his childhood friend kills the girl and steals her skill. This childhood friend wants to kill MC to atone for her sins and put an end to his misery. They meet in the dungeon again in final showdown, MC defeats her. At the end, he is sent back to japan but seems to retain all his abilities, which he uses to kill criminals.
Dungeon Seeker