Drooped, You'll find on Royal Road

Another one of my Diamond Series. In a normal highschool, where as all your classmates were summoned to another world to be heroes. But unfortunately our dear main character ended up with ERROR. So he was sent to a terrifying dungeon to perish. But who would have known that his sister and friend would go there to suffer with him, through the trials that awaits them. pls the cover art doesn't belong to me. Credit goes to the artist