Iwao Oguro/Relationships

Mrs. Oguro
Knuckleduster's wife appears to be bedridden and may be stricken with a terminal illness that has ravaged her body. Knuckleduster appears to love his wife very much and to be remorseful over their difficult past. As she is unable to speak due to her illness, it is uncertain how she feels about her husband.

Koichi Haimawari
The two vigilantes share a loose teacher-student relationship, with Knuckleduster helping Koichi with combat training and initially helping him use his quirk more effectively. It was Knuckleduster that suggested that Koichi change his hero name to The Crawler and pushed him to take his role as a vigilante. Despite this, the two are not especially close, with Koichi being generally terrified of Knuckleduster's predilection towards violence. However, unlike Kazuho, Koichi is able to acknowledge that although his methods are rough and seemingly excessive, Knuckleduster knows when to hold back when it comes to the force of his attacks, showing a respect for his skills as a vigilante.

Kazuho Haneyama
The two are fellow vigilantes, but their relationship can be deemed as a rocky one as both tend to bicker with one another on more than one occasion. Kazuho does not appear to tolerate Knuckleduster's aggressive and violent attitude, especially when it gets out of hand. Despite that, the two are capable of working together during Vigilante missions.

Tamao Oguro and Kuin Hachisuka
Unbeknownst to his fellow vigilantes, Kuin appears to be Knuckleduster's long-lost daughter Tamao - as she is controlling her body. He is deeply dedicated to tracking her down and freeing her from Kuin's control. Knuckleduster is aware that she is involved in the spread of the Trigger drug.

Giran
Knuckleduster appears to have a purely business relationship with the broker, obtaining equipment that's sometimes less than legal to deal with difficult Quirks.