Joe and Ranmaru never interacted in canon. The real Ranmaru died in his First Trial, and Joe was executed before he could meet the AI doll version of Ranmaru. AI Ranmaru is aware of Joe's existence, as he was programmed with the information that Joe was Sara's best friend and a non-participant, as well as overheard a bit about him from Midori. He knew enough about Joe to guess that the dog charm in the fifth floor classroom belonged to him.
In Chapter 3, Part 1 (Section B) if you go Kanna's route, it's shown that at some point Ranmaru tried to insert the Joe AI into himself.
As far as similarities go, both of them are male high school students who play a supporting role to Sara.
Both characters are much more commonly shipped with Sara, and the polyship combining Joesara and Ransara can sometimes lead to Joemaru being shipped as well. As Sara and Ranmaru are similar personality-wise, some may ship Joemaru because they prefer a slash ship with Joe.
Since Joe and Ranmaru have never met each other, the ship is based entirely on fan speculation about what their interactions would have been like.
A reason for this ship may be the height difference, with Joe at 174.8cm and Ranmaru most likely being below 164.5cm, as in one dialogue option he asks Sara not to make fun of his height, implying that he is shorter than her. Another may be the loud and optimistic personality matched with the quiet and serious personality. Joe is often associated with dogs, as he owns a dog keychain and is extroverted, and Ranmaru sometimes a cat for his introverted nature, making it a fun "cat and dog" dynamic.
The two's contrasting personality also comes out in their clothes. Joe's colour scheme consists of over 5 different colours, indicating his colourful personality, while Ranmaru's colour scheme consists only of different shades of white and grey, showing his more subdued nature. The contrasting outfits, and their representation of their personalities are another factor behind the shipping of this pairing.
Since Ranmaru and Joe are so different, they are considered a great example of the trope Opposites Attract.
- Joesaramaru refers to the ship between Joe, Ranmaru and Sara Chidouin.
|SHIPS||het||Joesara • Kaisara • Keisara • Mapledori • Maitaro • Naolice • Ransara • Ryojoe • Sousara • TiaRio|
|Alishin • Joemaru • Kaishin • Keishin • Keimishi • Keitaro • Kurusaka • Qkai • Soushin|
|Kusara • Naoreko • Naosara • Saramatsu • Saranzu|
|Kizuchi Sisters • Soukanna • Yabusame Siblings|
|CHARACTERS||m / f||Sara Chidouin • Shin Tsukimi|