Ōchi Fukuchi/Relationships

Yukichi Fukuzawa
Fukuchi has known Fukuzawa since they were young and are childhood friends who learned swordsmanship together in a government-run school of martial arts. It is implied Fukuzawa had always been one step ahead of him in life, which fueled their friendly rivalry and friendship over the years. They also seem to have a mutual friend named "Kin-chan" who Fukuchi said would be sad to hear that Fukuzawa had not yet married when he met with him at the military base upon his capture. Though Fukuchi has kept a friendly front for Fukuzawa over the years and also did him a number of favors for him and the Armed Detective Agency, he has actually held a hidden resentment for him. The reason for his hatred of Fukuzawa stems from his military days when Fukuchi participated in the war and suffered horrendous trauma in combat in addition to Japan's shameful defeat. He lamented the fact Fukuzawa did not join him on the battlefield, stating their paths split forever after this event. Though the details of this situation are still unclear, it is highly implied that Fukuchi blames Fukuzawa for Japan's loss in the war due to him assassinating the military war hawk bureaucrats and foreign correspondents who were in favor of keeping the war going and him not joining the war to assure Japan's victory, thus making all his efforts for naught. Fukuzawa, unaware of his best friend's hatred for him all the years, still trusted him to this day as the one man in the world he could trust the most.

Ranpo Edogawa
Fukuchi has known Ranpo since the day of the Armed Detective Agency's opening 11 years ago. During this event, Ranpo witnessed Fukuchi drink himself silly, make a loud scene, and urinate all over the agency's brand new placard. The event was so disturbing that Ranpo was genuinely taken aback by Fukuchi's behaviors, something he states he rarely ever does. On this day, Ranpo was told by Fukuzawa that Fukuchi is the one man in the world he could trust the most, thus causing Ranpo to trust him on blind faith alone, which ultimately led him to falsely believe Fukuchi could be trusted without question and didn't question him until his Ultra Deduction proved him otherwise. Despite Fukuchi mocking Ranpo for his childish nature and calling him a "brat", he acknowledges Ranpo's high prowess in observation and intelligence, even when he revealed himself as Kamui.