Keitaro Kikuchi is a central character known for his unwavering kindness and dedication to his simple but profound dream. At 21 years old, he operates his family's laundry business, the Western Laundry Kikuchi, with a singular goal: to make every piece of clothing in the world spotlessly clean. He is a young man with a gentle and earnest disposition, though he can be somewhat timid and is easily flustered, particularly in the presence of attractive women. His deep-seated desire to help others often leads him to act on pure, if sometimes misguided, altruism, frequently accepting tasks that others might refuse.

Keitaro's role in the story is that of an emotional anchor and a moral compass. He becomes an unexpected but crucial ally to the main characters, Takumi Inui and Mari Sonoda, when they cross paths during a delivery. Offering them room and board in exchange for working at his laundry, he transforms the shop into a central gathering place for the protagonists. Despite being a normal human without any special powers for most of the series, his courage and strong sense of justice push him into the heart of the conflict. On several occasions, he becomes frustrated by his friends' reluctance to fight and takes matters into his own hands, even stealing the Faiz Gear to confront the Orphnochs himself, believing it is his duty to protect others. A unique and notable trait is his sensitive nose; he has a pronounced allergy to dirt and grime, and he often sneezes whenever an Orphnoch is nearby, a quirk he himself attributes to sensing people with bad hearts.

His motivations are rooted in a philosophy of absolute acceptance. He fiercely believes that humans and Orphnochs can coexist peacefully. This conviction is severely tested when he discovers that his close friend, Takumi, and the woman he loves, Yuka Osada, are both Orphnochs. Unlike many others who view the creatures as monsters, Keitaro's friendship and affection remain unchanged after learning their true identities. His most significant personal relationship is with Yuka, who is initially his anonymous email pen pal. Unaware that the troubled young woman he meets and the charming "Yuka-san" he corresponds with are the same person, he develops strong feelings for her. When he finally connects the two, he accepts her completely, and they plan a date, a promise tragically left unfulfilled when Yuka is killed in battle. His other key relationships include his protective friendship with Mari, his unwavering loyalty to Takumi, and his complex association with the hostile Kamen Rider Kaixa, Masato Kusaka, with whom he often clashes due to Kusaka's manipulative nature.

Keitaro undergoes significant development throughout the narrative, evolving from a somewhat naive and simple laundryman into a resolute young man who actively chooses his place on the front lines of a war. While he never becomes a primary fighter like Takumi, he demonstrates immense personal bravery by facing down Orphnochs in his human form. This development culminates in the alternate timeline presented in the film Paradise Lost. In this story, Keitaro is a member of the Human Liberation Army. To protect his friends after Masato Kusaka is defeated, he consumes a dangerous experimental drug called Transform One-Shot, which allows a normal human to transform into a Kamen Rider at the cost of their life. He successfully transforms into Kamen Rider Kaixa, using the belt's power to destroy a powerful Orphnoch. Miraculously, he survives the transformation, but the Kaixa Gear is destroyed instead, turning to ash. This act solidifies his role as a hero who risks everything for his friends.

While Keitaro does not possess any inherent superhuman abilities of his own, his notable skills include a deep knowledge of laundry care and a surprising talent for household chores. His unique allergic reactions serve as an involuntary early warning system for the presence of Orphnochs. As a brief user of the Kaixa Gear in the Paradise Lost film, his physical abilities were augmented to superhuman levels, granting him the standard powers of Kamen Rider Kaixa, including increased strength, jumping ability, and access to specialized weapons like the Kaixa Blaygun. In the television series' final arc, he is also briefly entrusted with the Faiz Gear by Takumi, though his tenure as a rider is short-lived. In the years following the main events of the series, he eventually closes the family laundry shop and sets off on a journey to fulfill his dream on a global scale.