The story recounts the emergence of a powerful demon named Sucker and his transformation into a human form named Shu. As Shu, he develops a deep connection with a human girl named Lily, and together they fight against the invading monsters and demons. However, when faced with an impossible choice in a battle, Shu reveals his true form to save Lily and others. Ultimately, a closing portal consumes the monsters and demons, and Shu sacrifices himself, promising to return to Lily. The tale concludes with Lily's vow to bring him back, affirming that their love will prevail.