While Section 13 was primarily used to give Lucifer a human body, it also enabled the other Eight Demon Kings to receive one, which is how Amaimon received his human body. Although it was not ...

Specifically, a body from the batch of clones (of which Shiro originally was) that were made for the Demon Kings to inhabit. Amaimon, the King of Earth, also makes a brief appearance in this, I guess ...