Hideyoshi is Ken's best friend, nicknamed "Hide". He has a sharp intuition, so much so that while Ken tried to keep his ghoul identity hidden from him, Hideyoshi seemed to know something is weird about his best friend. Hide has proven to be intelligent and very observant, even figuring out that Rabbit was not Hinami like what CCG had first thought. He will also go to extreme lengths for those he cares about, like venturing to Aogiri's hideout and putting a tracking device on the torturous Yamori. After Ken disappeared, Hideyoshi joined the Anti-Ghoul forces in order to learn about his whereabouts, eventually being promoted to Rookie Investigator and partnered with Kotaro and Akira.