Nevula is the adoptive father of Alisa Southerncross, a character who appears in the later portions of the Sgt. Frog series. He is an amorphous alien being from a race that subsists by consuming other aliens. When in his resting or default state, Nevula takes the form of a spherical mass roughly three feet in diameter, with cat ears and a single red eye. However, he most commonly manifests as a pair of cat ears perched atop Alisa's head, serving as a constant companion and guide to her. His backstory establishes that he brought Alisa to life from a doll specifically to aid him in his search for food. His primary motivation is survival through feeding, which drives much of his and Alisa's involvement in the story, often placing them in conflict with the Keroro Platoon or other alien entities. Nevula's role in the narrative is that of a supporting character and sometimes antagonist, operating as part of a duo with his adoptive daughter. The two frequently collaborate, and Nevula's guidance or direct intervention is often key to their schemes. His relationship with Alisa is the central bond of his character; he is a parental figure who depends on her for mobility and direct interaction with the world. In terms of development, Nevula's character arc is tied closely to Alisa's, and his priorities gradually expand from mere feeding to protecting her well-being. Notable abilities include his capacity to change shape between the ear-like form and his larger spherical form, as well as the inherent traits of his species, though the full extent of his combat or other powers is not extensively detailed in standard reference materials. His role within a Christmas-themed episode further demonstrates that he is capable of directly engaging in battles alongside Alisa when the situation demands it.