Keitaro Kikuchi is a character from the movie Gekijōban Kamen Rider 555: Paradise Lost. He is originally depicted as a kind-hearted young man who works at his family's dry cleaning business. His most defining personal trait is a genuine and optimistic dream to make everyone in the world happy, a goal that reflects his fundamentally caring and supportive nature. Within his circle, he is known for his politeness, his strong sense of loyalty, and his willingness to help others in need, even at great personal risk.

In the alternate reality presented in Paradise Lost, Keitaro's background aligns with his established persona as a reliable friend. He becomes a member of the Human Liberation Army, a resistance group fighting against the dominance of Smart Brain and the Orphnoch. His primary motivation in the film is the same as his comrades: to fight for the survival and freedom of humanity. However, his actions are also deeply personal, driven by his protective feelings for his friends, including Takumi Inui and Mari Sonoda.

Keitaro's most significant role in the story occurs following the death of Masato Kusaka. To fill the void left by the fallen warrior, Keitaro takes up the Kaixa Gear, transforming into Kamen Rider Kaixa. This is a notable and dangerous act, as the Kaixa transformation system is known to be lethal for ordinary humans to use. Keitaro is able to become Kaixa by using a special one-shot serum, which temporarily allows a non-Orphnoch to safely utilize the Rider Gear. His tenure as Kaixa is brief but crucial, as he uses the armor's power to engage the enemy forces. A unique consequence of his use of the serum is that, after his transformation ends, the Kaixa Belt does not kill him; instead, the belt itself disintegrates into ash, cementing his temporary but heroic stint as a Kamen Rider. His relationships are central to his character, particularly his unwavering friendship with Takumi and Mari, for whom he is willing to risk his life. Throughout the film, Keitaro displays no notable superhuman abilities of his own. His primary strengths are his courage, his loyalty, and his ability to wield the Kaixa Gear in battle, using all of its standard weaponry and finishing attacks as Kamen Rider Kaixa.