Nain met Aoba along the shores by the church Aoba was left in care to. Nain first tells Aoba about his interest in traveling and the ocean before mentioning that he used to be just like Aoba. He tells Aoba that there are no wrong options in the world, and that at any time he could destroy the world and build a new one. Nain then decides to 'build a new world' for Aoba, by giving him a name and adopting him. It is later revealed that Nain met Haruka in Midorijima, finding her alone on a beach, just like Aoba, and helping her create a new world with him as well. Nain is known for his constant traveling, saying that he must hear different voices. It is also revealed that Nain was previously a test subject for Toue who managed to escape, becoming another reason for his travels.
Nain has short, auburn hair, fuchsia eyes and pale skin. It becomes noticeable on his talk-sprite that he has fangs. He wears a brown, long sleeved jacket that stops just below his waist, with large buttons. Underneath he wears a long sleeved maroon shirt. Nain wears black pants, with a large brown belt. His gloves and boots match his jacket.