Inmates
Nico
In the anime, not much is shown regarding Okina's relationship with Nico. He's blunt with him like he is with all inmates but he also cares for him like he does for all inmates. However in the manga, it's shown that he has a lot more trust in Nico than he does in the average inmate. While he won't let Uno or especially Honey or Trois so much as touch his daughter, KAGU-8, he allows Nico to rest his head on her lap. This is most likely because Okina sees him as an innocent and harmless kid.
Guards
Hajime Sugoroku
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Nanba Staff
Kazari Otogi
Kazari Otogi is Okina's wife. They have a dysfunctional relationship and argue constantly, even over petty things like putting worcestershire sauce on fried eggs instead of soy sauce. They often anger each other so much that they lose all sense of professionalism and fight while at work with inmates, their peers and their own daughter present. During that particular argument about eggs, it took KAGU-8 asking them about divorce to get them to stop. It's implied that this happens often. Okina describes Kazari's personality as nasty and says he can't stand her. Overall, they do not have a happy marriage and they would most likely get divorced if not for KAGU-8.KAGU-8
KAGU-8 is the brainchild of Okina and Kazari Otogi. Her creation was a collaborative effort between the husband and wife and they both see, treat and address her as their daughter. In the manga it was also shown that he is fiercely protective of KAGU-8, telling multiple characters he'll kill them if they lay a hand on her.