Caught up in a ritual performed by a God in another world, Eiji Choukai is transported to another world. The otherworldy God responsible for the ritual looked at Eiji potential incarnations, they pulled out Classes like those from "I reincarnated into a vending machine", but whereas there are normally several tens of Classes available for a person, the only Class avaiable for Eiji was "Parasite".
Having no choice but that one set-in-stone Class, Eiji reincarnates into his new world despondent. However, after using his powers he suddenly realized its potential. Using the parasite's powers, he finds he can amplify himself countless times by obtaining other people's powers. it could be that Eiji's level might rise too much.
