Kuroda is a childhood friend of Izumida, who calls him "Yuki." He calls Izumida by his first name, Touichirou. Kuroda was always the athletic one, while Izumida was clumsy. However, Izumida ended up surpassing Kuroda when they both joined Hakone Academy's cycling club.
Kuroda seems to enjoy messing with his teammate Ashikiba, acting tsukkomi to Ashikiba's boke. This actually causes Izumida to refer to the pair as a manzai act at one point.
Kuroda and Arakita's first meeting almost ended in a fistfight, but Arakita held back because Fukutomi helped reform his behavior. Arakita told Kuroda that, despite his athleticism, he was not cut out for cycling. Of course, this was a great insult to Kuroda, who succeeded at everything else. Kuroda later came to respect Arakita a great deal, and it is shown that Arakita thinks Kuroda has become quite skilled.