The story follows Nao, a young boy who prioritizes efficiency and avoiding trouble above all else. His summer vacation is dedicated to the simple task of completing a pet-keeping diary for his school research project, a task he approaches with minimal effort, opting for the easiest creature to care for: a rhinoceros beetle.
Chapter 3 introduces a peculiar situation where "Sura," a seemingly immortal mechanical goddess, falls ill with cold-like symptoms. The cause is traced back to her poor lifestyle habits, leading to Nao's "re-education" of her.
Chapters 4-12 detail Nao's encounter with a mysterious, glowing blue creature resembling a slime. While attempting to catch a rhinoceros beetle in a park, Nao stumbles upon a group of delinquents cornering something. He tries to avoid them, but a desperate plea for help from a girl's voice draws his attention. He discovers the source of the voice is a slime attached to his pants. When he tries to remove it, the slime burns him and falls to the ground, appearing to be crushed. The delinquents flee, leaving Nao to deal with the seemingly deceased slime.
To his surprise, the slime revives and begins to follow him. Nao attempts to care for it, giving it water and salt, and is amazed by its energetic bouncing. He tries to communicate with it, but it only responds with bounces. He considers selling it for money but it disappears and reappears behind him with incredible speed, evading his attempts to catch it. Despite its elusiveness, it eventually allows Nao to pick it up easily.
The slime, which Nao nicknames "Sura," follows him home. Nao's mother, initially surprised, accepts Sura into their home. Sura proves to be an intelligent and helpful creature, learning to perform chores and even cook. Nao, initially reluctant to keep Sura, finds himself growing accustomed to its presence. Sura communicates through written messages and expressive bouncing, and Nao learns that Sura is incredibly durable and can manipulate objects with telekinesis.
Over the next three years, Sura becomes an integral part of the Nao family, assisting with household tasks and even preparing meals. Nao's mother has kept Sura's existence a secret from the neighbors, but eventually, the secret is revealed, causing Nao some distress. Despite his initial reluctance, Nao develops a bond with Sura, even using it as a pillow.
The narrative also touches upon Nao's desire to avoid attention and difficult situations, particularly regarding school club activities, which he skillfully evades through clever excuses and manipulation. He also reflects on his past, including a humorous incident where his fabricated slime-keeping diary earned him an award. Nao's interactions with his classmate Hina and his mother reveal his complex personality, his desire for a peaceful life, and his growing acceptance of Sura. The story concludes with Nao and Sura preparing for a trip to the beach, highlighting their unusual but established companionship.
