Hold on, Who's Mammon?

In a universe where Mammon urged Diavolo to turn the punishment to him instead of Belphegor, His soul gets sent to a human's body as the punishment.

Surprisingly, He still has his powers. Unknowingly, of course. His memories got wiped, and he awoke as a random shut-in. Several Decades later, Mammon (Or should I say Marco?) realized his.. long lasting life, and decided to be a model due to being bored.

As the months went by and also as his appearance refused to falter, he disappears, only to be teleported into the devildom, as the human exchange student. How does he deal with the phenomenon where the demon brothers cling onto this doppelgänger, not knowing he is the actual brother?

(except for a few characters.. they'll ALL know soon dw)

(Crossposted from AO3, TUMBLR)