Ranpo Edogawa/Relationships

Yukichi Fukuzawa
Fukuzawa took Ranpo in as an orphan twelve years before the story begins. Fukuzawa first met Ranpo after running into him on a job where Fukuzawa was working as a bodyguard for a CEOs murder. Fukuzawa, impressed by Ranpos ability to solve the case immediately, takes Ranpo to a restaurant to repay him.

From there, Ranpo pesters Fukuzawa until he takes Ranpo with him on his next job at a theater. Halfway through the play Ranpo starts a commotion, with Fukuzawa ultimately storming outside the theater with the boy. After discovering that Ranpos loneliness and anger towards other people was caused by Ranpo genuinely believing he was no different nor special than others, Fukuzawa then tells Ranpo a white lie; that he’s an ability user. Ranpo, filled with newfound confidence, solves the case at the theater.

However, Ranpo, at some point while luring out an organization behind the case puts himself in danger. When Fukuzawa came to save him, he gets incredibly upset with the boy for putting himself in harms way resulting in him slapping Ranpo. Fukuzawa then consoled him.

They stayed together for a while, Fukuzawa going to bodyguard missions (and ultimately not needing to protect anyone due to Ranpo solving the threat), and Fukuzawa accompanying Ranpo on cases, before Fukuzawa realized there was an issue. Ranpo was brilliant but weak, and would need someone to protect him while he solves crimes. And while Fukuzawa could do so, there would come a time where he couldn't. And so with that, the Armed Detective Agency was formed.

Ranpo and Fukuzawa are shown as very close, and their relationship being hinted towards a parent guardian one. Fukuzawa, though sometimes annoyed with Ranpo puts up with it out of deep care and respect for him. As for Ranpo, he seems to have a deep seated admiration for Fukuzawa, doing things simply for the sake of being praised by him and becoming incredibly depressed when harm befalls him.

Akiko Yosano
Its mostly seen that Yosano seems to be close with Ranpo due to him assisting her out Fukuzawa and Mori's fight on who's going to have her. Furthermore, she's also with Ranpo when they arrived at the location where Edgar Allan Poe invited Ranpo for another competition on solving his novel.

Osamu Dazai
Ranpo and Dazai are shown to be on good terms with each other. Both have eccentric personalities and seem unbothered by it which is shown during the Yamagiwa's murder case when Ranpo simply reacts to Dazai's theatrical attitude by stating that he's always like that and Dazai trying to calm down a furious Minoura by explaining that Ranpo is just being himself and that he doesn't mean any harm.

The two are also shown to be the most intelligent and most capable strategists in the Armed Detective Agency as they worked together during the Guild Arc to come up with a plan to take down the Moby Dick. On top of that, despite Ranpo stating that he is better than Dazai, they both seem to respect each other's intellect with Dazai admitting that he only found half of the evidence on the Yamagiwa's murder case and Ranpo stating that facing Fyodor Dostoevsky was complicated as it was like facing Dazai.

Kyōka Izumi
Despite not having many interactions, they appear to be close with each other as Jun'ichirō explained that Ranpo was the one in the Agency who was the happiest that Kyōka was here when she first arrived. They are also shown eating candies together which causes Atsushi to think that they look like elementary school siblings.

Chūya Nakahara
Chūya and Ranpo have briefly interacted a few times, most notably when Ranpo stuck Chūya in a book made by Edgar Allan Poe. Ranpo calls Chūya Mr. Fancy Hat, rather than his name.

Edgar Allan Poe
Six years ago, Poe and Ranpo took a case together in which they decided to have a detective battle. However, Poe lost and fell into a depression where he cut off ties with his family and friends. For six years afterwards, he started working on a plot to get back at Ranpo. He joined the guild just to challenge Ranpo.

But, even though Poe challenges Ranpo (with Akiko Yosano) again, he doesn't win. Even more, Ranpo seemed to not have remembered their original detective battle at first, which greatly upset Poe. Though, after their 'fight', Ranpo remembers Poe and exclaims that it was the first time he'd been pushed that far by another detective.

Minoura
Minoura was initially hostile towards Ranpo as he believed that he was incompetent and also disliked his arrogant behaviour. However, after Ranpo was able to solve the Yamagiwa's murder case, Minoura apologized for doubting his abilities and told him that he will contact him if he ever has trouble with another case to which Ranpo replied that he will gladly help him.