TV Special
Description
Ten is an Oni toddler from space and Lum's maternal cousin, since his firefighter mother is the younger sister of Lum's mother. Due to his mother's demanding career and rare Earth visits, Ten primarily lives under Lum's care at the Moroboshi home. He initially arrived to vet Lum's fiancé, Ataru Moroboshi, instantly deemed him unworthy, and moved in to plot their separation.

Sporting green hair and a small horn on the back of his head, Ten wears a yellow tiger-striped diaper. He displays a dual personality: mimicking Ataru's flirtatious behavior around pretty girls behind an "innocent baby" act, yet acting bratty towards male students, especially Ataru, earning him the nickname "Jariten" (Bratty Sky). He retaliates against mistreatment with fire-breathing, sometimes causing significant damage like burying Tomobiki High School. His abilities include flight (speed similar to Lum's) and generating massive fire from his mouth.

Ten's pyromania sharply contrasts his firefighter mother's profession. He hides this ability during her visits to avoid punishment, as she despises arsonists. Ataru exploits this fear, using a fire bell she provided to summon her under false pretenses and intimidate Ten. Despite his nature, Ten shares a close bond with Kotatsu-neko, often relaxing together after meeting on the Moroboshi staircase.

Ten harbors romantic feelings for Sakura, the school nurse and priestess, repeatedly asking her on dates and proposing they "expose their naked selves." Sakura consistently rejects him due to her vocation and age, yet Ten remains devoted, confiding in her when fearing Lum's disapproval and reacting jealously to Ataru flirting with her. His relationship with Lum is deeply trusting; he relies on her for protection against Ataru and spirals into distress if he believes she hates him, like after accidentally burning her hand-knitted scarf.

In "The Obstacle Course Swim Meet" OVA, Ten attends Tomobiki High during the chaotic swim competition organized by the principal, featuring obstacle navigation with summer homework exemption for winners. He participates but plays a peripheral role amidst the central chaos caused by Oyuki's multiplying, freezing wind chimes, not advancing to the final stages.

Ten speaks in an Osaka dialect for unspecified reasons. He cannot swim, leading Lum to teach him by throwing him into a pool with a 50-ton barbell. His mother's absenteeism contributes to his obnoxious tendencies, feigning innocence during her visits. Despite this strained dynamic, Ten cares for her, as seen when he searches for a Mother's Day carnation to gift her, alleviating her fears of his delinquency.