Ryuuzou Takehara, a doctor on Sentan Island, possesses a tall, larger build, light tan skin, short shaggy brown hair, brown eyes, and a thick brown mustache. His serious and straightforward demeanor contrasts with his cluttered lifestyle and unkempt medical office. Married to Fusa Takehara, they live separately due to marital strain but maintain a functional relationship for their son, Akiyuki Takehara, who frequently delivers meals and assists with clinic chores.

Seventeen years before the main events, Ryuuzou served as a Northern Government military doctor during the Battle of Barador. There, he conducted experiments injecting Hiruko endosymbionts into fatally wounded soldiers as part of humanform weaponization research. This past involvement burdens him with deep regret, symbolized by ututu seeds he retains from that era.

After a terrorist attack involving the suicide bomber Nazuna, Ryuuzou's son Akiyuki disappears. Ryuuzou and Fusa temporarily set aside their estrangement to search, with Ryuuzou visiting every island hospital. His concern extends to Akiyuki's friend, Haru Nishimura, whom he advises against undue worry. As Sentan Island militarizes, Ryuuzou is recruited by Prios Sukakki for his expertise, assisting in an anti-humanform research laboratory.

Ryuuzou displays a complex moral compass. He sustains Nazuna—the bomber linked to Akiyuki's transformation—on life support despite her role. His philosophy emphasizes introspection: "A question without an answer is truth. Yet, people must continue to question themselves; it's their nature." This outlook drives actions like saving Commander Kagisu after a suicide attempt, refusing his wish to die, and providing ongoing care. Ultimately, Ryuuzou adopts Nazuna as his housekeeper, reflecting his commitment to redemption and compassion.