Kuroda created the Hybrid Children, artificial beings that are neither fully machine nor human and require love to develop emotions and grow. He stands approximately 180 cm tall with a slim, muscular build and medium-length black hair. As an adult, he typically wears a dark blue robe, with bandages worn beneath it on his arms and neck; the neck bandage is believed to conceal the headband of his deceased childhood friend, Tsukishima. In his youth, he wore his hair in a ponytail. During childhood, Kuroda displayed a stubborn nature that softened into a teasing but caring personality towards his friends. He formed a close trio with Tsukishima and Ichi Seya, sharing a deep bond despite Tsukishima's frail health. Kuroda harbored romantic feelings for Tsukishima, feelings implied to have been mutually confessed before Tsukishima's death. The two shared an intimate encounter prior to Tsukishima committing seppuku to save his clan after a war. Tsukishima's death left Kuroda heartbroken, and he never moved on from this loss. Kuroda's grief inspired the creation of the Hybrid Children. His first prototype bore a striking resemblance to the young Tsukishima. He came to terms with his emotions when this prototype replicated Tsukishima's gesture of offering a sakura branch, mirroring an earlier act from their past. Despite the tragedy, Kuroda maintained a lifelong friendship with Seya. His work on the Hybrid Children reflects his exploration of love, loss, and the human capacity for emotional bonds.