In a realm where the hero has vanquished the Demon King and tranquility has been restored between humans and demons, Shidan, a demon enjoying a leisurely existence as a wandering painter, unexpectedly becomes the target of the Royal Knights. The charge against Shidan is that he instructed the Demon King in martial arts, leading to the Demon King's swift rise in power and subsequent disturbances in various regions. Despite being attacked by the knights due to suspicion, he easily defeats them with his worn sword, showcasing a strength that even the knight commander cannot rival. Shidan yearns for a peaceful life as an artist, yet is ensnared in a 'Covenant Ring' by the hero, who is disguised, and is reluctantly compelled to join him on a quest to defeat the Demon King...!?