At his wit's end, a landlord breaks into the apartment of a tenant who stopped paying rent — and discovers a gruesome, seemingly impossible murder.

A little boy goes into the Millenarianism Research Institute saying he wants to become a demon, but Akuma Kun immediately throws him out.

When Shingo — aka the first Akuma Kun — is sealed away, the father and son Mephistos set out to rescue him, while Akuma Kun takes a different approach.

Akuma Kun, Gremory and Mephisto III enter the barrier to save Shingo. But first, they'll have to confront Strophaia, an old enemy from Ichiro's past.