Three months after being transported from his part-time job at a Chinese restaurant in Wakayama to the magical realm of Twisted Wonderland, the magicless Yuuta Mito has settled into an unusual life as a student at the prestigious Night Raven College. Alongside his companions Grim, Ace Trappola, and Deuce Spade, Yuuta navigates the challenges of a school for magicians despite lacking any powers of his own.

Following exam season, a bizarre affliction strikes numerous students, causing sea anemones to sprout from their heads. Yuuta discovers that his friends and many others have become indentured servants to Azul Ashengrotto, the housewarden of Octavinelle, as a result of magical contracts they signed. Azul runs the Mostro Lounge, a restaurant operated largely by students bound to his service, and his unique magic allows him to grant any wish in exchange for something his clients treasure most.

Octavinelle dormitory draws its inspiration from The Little Mermaid, founded on the compassion of the Sea Witch, and its members reflect this theme. Azul, whose true form is part-octopus, was once a bullied child who transformed himself through sheer determination and now masks deep insecurity behind a calculating and courteous exterior. His closest allies are the Leech twins, Jade and Floyd, childhood friends from the Coral Sea who serve as his vice-housewarden and enforcer respectively, with the twins capable of revealing eel-like merfolk forms. The dormitory itself is located beneath the ocean, accessible through magical transportation bubbles.

Since Yuuta never signed any agreement with Azul, he remains unaffected and becomes the key to rescuing his friends. The narrative follows his efforts to break the contracts without magic, leading to a high-stakes confrontation. The climax sees Azul pushed into an Overblot, a dangerous state where a mage loses control when their emotional scars and insecurities overwhelm them, causing his eyes to go dull as the corruption takes hold. The twins, despite their previously claimed transactional relationship with Azul, ultimately return to stop him and help their friend recover.

After Azul returns to normal, the group visits the Atlantica Memorial Museum to return a stolen class photo, a relic of Azul's painful childhood memories of being mocked as a slow, chubby octopus who cried ink. There, Azul confesses his admiration for the Sea Witch, who owned her past misdeeds and earned recognition through actions rather than erasing history. Yuuta offers Azul unexpected kindness, praising his hard work in compiling a century of test questions and noting that giving their headmage such difficulty requires true villainy. The story concludes with a picnic where Yuuta shares his cooking with everyone, followed by the group helping at the Mostro Lounge, suggesting Azul has begun to accept both his past and his genuine connections with others.