One hot summer night in Sky Oriels, Marshall hears a distressed scream from an alleyway. Investigating, he finds a boy being attacked by a sinister man trying to steal a spiritual sword. Marshall intervenes, but the sword's hilt freezes to his hand, trapping him in icy clutches. Only the sword's master, the snow deity Wyn, secluded in the forbidden forest, can help. Marshall learns that Wyn was isolated for a mysterious crime, but the snow deity seems unwilling to reveal it.

As they witness a demon invasion, the two have no choice but to unite to survive. Meanwhile, Marshall discovers his true origins as the son of the Demon Overlord and becomes a target for Lord Chioni, who frames him for crimes deserving execution. To clear his name, they must take down Lord Chioni, however it proves to be a difficult task.