The two didn't had much interactions in the main game as Ryoma died in chapter 2. Shuichi asks various questions to Ryoma during Free Time Events like about his friends, love interest, and family. In their one of the interactions, Ryoma suddenly realized that Shuichi wanted him to return to play tennis for his sake. He warned Shuichi to not make him play tennis anymore. Even though Ryoma wanted Shuichi to leave him and his past alone, Shuichi didn't intend on throwing out Ryoma's relationship away. With such Shuichi dedication for him, Ryoma decides to teach him to play tennis.
In Love Across the Universe, Ryoma talked to Shuichi about a cat he used to have before going to prison and his strong relationship with it. Ryoma worried that the cat has already forgot about him. Shuichi affirms to Ryoma that his cat is being well cared by his new owner and denies to him about being forgotten by the cat.
In the School Sport Festival, Ryoma decides to play a game of table tennis. Despite it not being the real tennis, he believes holding the paddle brings back memories. He play a match against Shuichi, and as the Ultimate Tennis Player, we obviously won. Shuichi says that he never stood a such against Ryoma. Ryoma tells him that as a detective, Shuichi's got good instincts, but his reflexes "still have a ways to go". Shuichi says that it looked as if Ryoma was actually having some fun. Ryoma says that Shuichi shouldn’t think that unless he needs to get his eyes checked. But despite that, Ryoma does think that it was a nice game to play.
The ship mostly sailed due to their interactions in the free time event. Even with the warning, Shuichi didn't wanted to leave his relation with Ryoma and wanted to make him play tennis again.
- Ryoma's relationship with Shuichi on Danganronpa Wiki
- Shuichi's relationship with Ryoma on Danganronpa Wiki