This gun is from the manga/anime Gantz. I’m not a fan of Gantz so can’t tell you much about it.
From what I hear, Gantz is a gory anime with lots of violence and steamy uncensored scenes in it.
The story is about two young man who got hit by a train when trying to save an old man. Upon death they were locked in a small room with a Gantz sphere.
Gantz sphere contain mission on which the choose people need to accomplish. Their mission is to kill alien on earth and they are given equipment and weapons with super strength power.
Model designed by Martinmilo_18