Hatsu Kominato is the paternal grandmother of the main character, Ruuko Kominato, and serves as her primary guardian. She lives with Ruuko and her older brother, Ayumu, in their apartment. Her own daughter, Miyako Kominato, is the mother of Ruuko and Ayumu, but due to Miyako's neglect of her children, Hatsu took over their care, believing her daughter was unfit to be a parent.

Hatsu is an elderly woman with grey hair that she often keeps in place with a red headband, a face marked by gentle wrinkles, and a kind, perpetually smiling expression. Her wardrobe typically consists of a white turtleneck paired with a brownish-green sweater, and she is slightly shorter than her granddaughter. Her demeanor is consistently warm and caring, with a particular soft spot for Ruuko, whom she dotes on openly. She is perceptive and worries about Ruuko's well-being, especially her difficulties in making friends after moving to a new school. When Ruuko does begin to bring friends home, like Yuzuki Kurebayashi, Hatsu's relief and joy are evident; she goes out of her way to welcome them, such as buying an excessive amount of cakes to celebrate the new friendship.

Despite her gentle nature, Hatsu possesses a sharp and unshakable practical wisdom. She speaks frankly, especially when it comes to her family. She is known to be a devoted player of the WIXOSS card game, often playing with Ruuko under a system of bets where the loser must perform household chores. Her skill at the game is remarkably high; she is able to consistently defeat her granddaughter, who is regarded as an exceptionally strong Selector, without losing a single match. On one occasion, she played six consecutive games against a challenging opponent named Chiyori and won every one of them, leaving her opponent bewildered.

Hatsu's role in the story is that of a stable, grounding presence in Ruuko's tumultuous life as a Selector. She provides a home and a sense of normalcy, often being the person Ruuko returns to after her battles. She does not pry into Ruuko's secrets but offers quiet comfort and understanding. For instance, when Ruuko comes home late and distressed, Hatsu does not demand answers, instead telling her that she can talk when she feels ready. Her counsel is sought after and influential; she encourages Ruuko to follow her own heart regarding her wishes, reinforcing that whatever Ruuko truly wants is worthwhile. In a flashback during the film Selector Destructed WIXOSS, she is shown to be a stern moral compass for her own daughter, immediately scolding Miyako for blaming her children for the failure of her marriage.

Key relationships define Hatsu's position in the narrative. Her bond with Ruuko is the most central, characterized by mutual affection and playful rivalry over card games. With her grandson Ayumu, she shares a lighter relationship, often creating customized video games for him to play. Her relationship with her estranged daughter, Miyako, is one of disappointment and protective distance. Hatsu has prevented Miyako from having direct contact with Ruuko and speaks of her with contempt, refusing to let her near the granddaughter she once neglected.

Over the course of the story, Hatsu does not undergo a dramatic personal transformation. Instead, her development is seen in her subtle adaptation to Ruuko's changing life. Initially focused on Ruuko's isolation, she shifts to a role of quiet support as Ruuko becomes more involved in the dangerous world of Selector battles. Her unchanging nature is her strength; she remains a reliable, perceptive, and unconditionally supportive anchor. Her notable abilities lie not in supernatural power but in her exceptional talent for games, her profound understanding of her granddaughter's emotions, and her formidable, undefeated record as a casual but masterful WIXOSS player, a fact that has earned her a reputation among fans as a hidden "strongest" character.