A desolate land stretches out from the city of poverty. A motorcycle speeds recklessly, blowing clouds of sand and dust. The rider is the protagonist of this story – he has neither a name nor a past. All he has is his ring name, “Junk Dog” and a technique for rigging MEGALOBOX matches with his pal Gansaku Nanbu, which they use to support their hand-to-mouth lives. JD is bored, resigned, and unfulfilled. Yuri has been the reigning champion of MEGALOBOX for the past few years. He has the skills and presence of a true champion. This is a story of JD and his rival, Yuri.

17 years ago, immortals first appeared on the battlefields of Africa. Later, rare, unknown new immortal lifeforms began appearing among humans, and they became known as “Ajin” (demi-humans). Just before summer vacation, a Japanese high school student is instantly killed in a traffic accident on his way home from school. However, he is revived, and a price is placed on his head. Thus begins a boy’s life on the run from all of humankind.