Kyoko Ariyoshi operates as an agent for Mishima Heavy Industries, executing missions under CEO Akiko Natsume's command. Teamed with colleague Arisa, she pursues objectives centered on capturing the android Nuku Nuku and aiding Akiko's efforts to reclaim custody of her son, Ryunosuke. Kyoko typically displays a more measured demeanor than the impulsive Arisa, sometimes providing a voice of reason within their partnership.

Their assignments frequently pit them against Nuku Nuku, Ryunosuke, and his father Kyusaku Natsume, utilizing Mishima's experimental technology. These encounters often conclude in comedic failure. Budget cuts at Mishima Heavy Industries drive some actions, including an incident where resentment over reduced circumstances leads Kyoko and Arisa to sabotage Nuku Nuku's restaurant job.

Kyoko appears throughout the franchise. She features in the original OVA series, participating in Akiko's schemes across its six episodes. Her role continues in the television series as an operative carrying out Mishima missions. She also appears in the spin-off *All Purpose Cultural Cat Girl Nuku Nuku DASH!*, maintaining her position within Akiko's organization. Across these series, OVAs, and spin-offs, Kyoko remains a persistent, though often ineffective, operative loyal to Akiko, characterized consistently as a supporting antagonist engaged in comedic confrontations alongside Arisa.