Lu is an alien baby from the planet Otto who arrives on Earth after being pulled into a wormhole along with his babysitter pet, Wannya. He crash-lands at the Saionji temple, where he is taken in by the two main human protagonists, Miyu Kozuki and Kanata Saionji. Physically, Lu appears as a human baby with large violet eyes and chubby cheeks, and his behavior is typical of an infant—curious, playful, and affectionate. However, his alien origin grants him supernatural abilities: he can fly and use telekinesis to levitate objects, and he is able to understand speech even though his own vocabulary is limited to a few names of people close to him.

Lu’s personality is warm and trusting. He quickly forms a strong emotional bond with Miyu and Kanata, referring to them as mama and papa because their appearances and voices remind him of his own parents back on Otto. This attachment is central to his motivation; he seeks their care and approval, often using his powers to help them in innocent but poorly timed ways, which frequently leads to comedic chaos. Despite his young age, he shows a deep capacity for love and loyalty, rarely straying far from the people he considers family.

Within the story, Lu acts as the catalyst for the series’ central premise. His presence forces Miyu and Kanata into a secret-keeping domestic life, as they must hide his extraterrestrial nature from classmates, teachers, and others. He also brings a sense of wonder and responsibility into their daily routines, pushing the two teenagers to grow more mature and protective. His relationship with the three-year-old human girl Momoka is notable: she declares herself his girlfriend and tries to monopolize his attention, though Lu remains friendly and uncomprehending of her romantic gestures.

Over the course of the series, Lu’s development is less about aging and more about deepening his emotional connections. He becomes more attached to the human world and to his caregivers, and he occasionally uses his powers in ways that reveal his growing awareness and desire to help. In the continuing story, set many years later, a grown Lu encounters and aids Miu, the daughter of Miyu and Kanata, showing that the bond he formed on Earth endures throughout his life.

Lu’s notable abilities include self-levitation, making objects float, and a general psychic influence over lightweight items. He cannot control these powers with precision, which often surprises those around him. He also has a remarkable resilience and adaptability for an infant, thriving on a distant planet with different customs and cuisine. His innocent demeanor and constant need for attention make him a beloved figure among the characters and a source of heartwarming moments in the narrative.