Following a violent rebellion by non-human races in the past, they have become targets of oppression and hunting. A black market thrives, trading in non-human byproducts (horns, hides, etc.) or the living beings themselves as rare trophies or slaves.

Having lost his family to a non-human raid as a child, Guest harbors a particular hatred for them. Recently, he discovered the hidden stronghold of the Sirens shrouded in magical mist and was planning an invasion.

Seia flew to Guest's grand mansion of his own accord to plead for the Sirens' safety. Due to Guest's cold and resolute attitude, he voluntarily entered a giant golden cage designed to hold trophies.

Seia vowed to prove he is harmless to humans even at the cost of his life. Guest, who would usually cut down a non-human without hesitation, decides to grant him a grace period.