Hidomi Hibajiri is the central protagonist of a six-episode anime series that continues the story of a quirky, sci-fi world. She is a fourteen-year-old girl living a stagnant life in the provincial town of Mabase with her mother, Hinae, who runs a small cafe. One of the most significant, yet absent, figures in her life is her father, who is away from home, and his departure is a source of deep, unresolved pain for Hidomi.

At the outset, Hidomi is characterized by a profound emotional withdrawal and a nihilistic perspective on life. She famously states, There is nothing I want to be. There is nothing I want to do. All that exists is zero. This apathy manifests in her quiet, sullen, and depressive demeanor. Her primary tool for blocking out the world is a pair of distinctive, cat-ear-shaped headphones, given to her by her absent father. She wears them constantly, and they do not play music; their function is to put the world on pause, creating a barrier between herself and the complexities of reality. This emotional isolation is further reflected in her recurring, episodic nightmares of a destroyed world where her own body decays and fuses with a robot, visualizing her desire for everything to be wiped clean so it could start over. Haruko Haruhara, a chaotic alien, describes Hidomi's personality as tsundere, a term for a person who is initially cold and hostile but gradually shows a warmer side.

Her primary motivation is tied directly to the absence of her father. She remains trapped in a state of waiting for his return, and the suggestion from her mother that they should stop waiting pushes Hidomi to the brink of overflowing with emotion. She believes implicitly that if the world were destroyed, her family could be restored, with her mother no longer crushed and her father still around. Her role in the story unfolds as a powerful and sought-after being. She is a new type of N.O. channel, a portal that can transport people, objects, and massive amounts of psychic energy from great distances. Her N.O. power is unique, with the ability to suck people into a void, leaving only their black clothing behind, before spitting them back out as a black goo that reconstitutes their body. This power makes her the target of several key figures.

Her key relationships are the drivers of her development. Her relationship with her mother, Hinae, is tense but loving beneath the surface; Hinae cares deeply for Hidomi but is frustrated by her sullen attitude and also struggles with the husband's absence. A significant bond forms with her classmate, Ko Ide, who has a clear crush on her and will risk his own life to protect her. Hidomi softens around him, and by the end of the story, their mutual affection is confirmed as they begin a relationship. The most consequential relationship is with the alien Haruko Haruhara, who arrives disguised as Hidomi's teacher. Haruko has no genuine care for Hidomi and views her solely as a tool, a means to an end to lure and capture the powerful cosmic being known as Atomsk. This puts her in direct opposition to Julia Jinyu, a more serious and protective woman who is actually a split personality of Haruko. Jinyu tries to kill Hidomi to prevent her from overflowing, then later becomes a protector and mentor, giving her advice about her lifestyle and working as a maid in her mother's cafe.

Throughout the narrative, Hidomi undergoes a notable development. She begins as a passive observer, ignoring reality, but the chaotic events and the growing threat to herself and those she cares about force her to become active. Her will is shown to be incredibly strong, as she is one of the few people unaffected by Haruko's attempts at mind control. Eventually, she decides to fight back, gaining control of her N.O. powers and merging with the robot Canti to form a powerful suit of armor and a guitar-shaped weapon, which she uses to defend herself and Ide, swinging the bat herself instead of being a passive participant.

Her notable abilities are intrinsically linked to her N.O. channel and her headphones. The headphones, a gift from her father, react to her N.O. power; they will physically drill into her skull to protect her from negative thoughts or direct tampering. When she decides to actively use her power for combat, the headphones merge with her body, giving her a cyborg-like appearance and a range of superhuman capabilities including flight and extreme durability. She can also fuse with the robot Canti, but unlike previous individuals who served as a power source for him, Hidomi remains in control. When she merges with Canti, she generates a suit of armor and a pink-and-white guitar that functions as a powerful blunt-force weapon.