Hozuki Ferrari is the thirteen-year-old youngest sister of the Ferrari family and a junior high school student. As a direct descendant of the astronomer Galileo Galilei, she is a prodigy whose singular genius lies in science and engineering. Despite her remarkable intellect, Hozuki often comes across as flighty and lacks confidence in her own abilities, which can make it difficult for her to persist with new endeavors. Her personality is generally reserved and quiet, and she has a shy, apologetic demeanor, even when her actions inadvertently cause destruction. However, beneath this timid exterior lies a resolute core, as she is often the first of the three sisters to take decisive action and stand up for what she believes is right. Hozuki has a deep fondness for Japanese culture and food, particularly Japanese confections, and maintains a strong attachment to her pet goldfish. This fondness heavily influences her aesthetic, as she designs her most advanced machines to resemble giant, flying mechanical goldfish.

Within the story, Hozuki acts as the team's inventor and engineer, creating the gadgets and vehicles essential for her family's survival and quest. Her most notable creation is the Galileo, a large, airship-like mecha shaped like a goldfish that serves as the sisters' mobile base. Her arsenal of inventions is versatile and dangerously effective, ranging from homing missiles to machine guns, though she is often reluctant to use them. Her role as the family's technological backbone is crucial, as her creations consistently turn the tide in their encounters with antagonists. Her personal motivations are deeply tied to her family; while she initially comments on her family being fractured, she is fiercely protective of her siblings and parents, and her actions are largely driven by a desire to keep them safe. A significant part of her personal journey involves her growing understanding of love. By deciphering the clues left behind by her ancestor, which turn out to be love letters, she begins to ponder the nature of love. This culminates in a poignant time-travel sequence where she meets a young Galileo Galilei, and the two develop a mutual affection, leading her to realize that the love letters were addressed to her.

Hozuki's key relationships are primarily with her two older sisters, Hazuki and Kazuki. Despite their distinct personalities and initial estrangement, the bond between the three strengthens as they face danger together, with Hozuki often looking to them for support while also proving her own reliability. Her relationship with her inventor parents, Sylvia and Geshio, is also significant, as she inherits her scientific aptitude directly from them. The death of a friend, Leo, unnerves her deeply, and this trauma later fuels her resolve to stop a villainous rampage, marking a key point in her development from a hesitant child to a more resolute protector. Throughout the series, Hozuki matures from a shy, uncertain girl into a more confident individual, learning to trust not only her incredible abilities but also her own heart and the power of the bonds she shares with her family.