Kotomi Hiyama is the owner and manager of the Enohana Bathhouse, a public bath struggling to stay afloat, while also holding a job at a video production company in the city center. She is thirty years old, wears simple blouses and skirts, and keeps her shoulder‑length black hair loose. During her college years, when alien arrivals on Earth were still treated with some anticipation, she took a course on interplanetary business, but the excitement faded once it became clear that extraterrestrial contact would not change everyday life. Out of a longstanding fondness for the bathhouse she visited as a student, she purchased it to prevent its closure and built a home for a small, eccentric household.

Her personality is primarily calm, kind, and unflappable, yet she is also fiercely competitive. When provoked—such as by a young girl’s dismissive remark about the bathhouse tournament prizes—she abandons any promotional goals and marshals her staff to defeat all challengers. She can be forgetful at times but remains sincere and bright, someone the people around her look up to and rely upon. Underpinning her demeanor is a deep pragmatism: she approaches the bathhouse’s red balance sheets with methodical attention, night after night, and when the financial noose tightens she begins discreetly preparing to sell rather than let the place collapse unchecked.

Kotomi’s relationships reveal a maternal side that belies the simple role of boss or landlord. She allows Mayuko Chigasaki to live rent‑free above the bathhouse in exchange for a few hours of cleaning work, and she frequently offers Mayuko calm, life‑directing advice, notably the truth that only Mayuko herself can decide her own path. She tolerates the antics of the alien NieA but sets firm boundaries when demands become unreasonable. She remains seemingly unaware of the boiler operator Nenji Yoshioka’s crush on her and overlooks his pyromaniac tendencies, while tenderly supporting the aging flower‑tending matron Momo Enoshima. These dynamics make the Enohana Bathhouse less a business and more an extended family under her care.

Over the course of the story, Kotomi faces a defining internal struggle. The constant financial losses push her into long, liquor‑fueled nights with the account books, and she sinks into a subdued depression. Yet even at her lowest she does not lash out at those who depend on her. She makes practical arrangements to sell the bathhouse but makes sure everyone knows what lies ahead, demonstrating that her concern is for the people, not just the property. In the end her persistent belief in her own capabilities helps reverse the economic tide, and she cancels the sale at the last moment, preserving the one place where she feels the world is right. Her notable abilities include business management, organizational skill, maintaining calm leadership under pressure, and balancing two demanding careers without sacrificing the warmth of the makeshift family she has gathered.