Daichi has a close relationship with Sugawara, being one of the other third years and the most observant member of Karasuno. Daichi and Sugawara have been friends for years and seem to know each other very well and rely on one another as teammates and friends. Suga also seems to be the only member of Karasuno immune to Daichi's intimidation. It is also seen that Suga is the only one who can lecture Daichi.
Daichi has a mostly-friendly relationship with Karasuno's ace spiker, though he gives Asahi a lot of grief. He's even stated that Asahi is the only one he isn't fundamentally kind to, though Daichi also shows obvious respect for him (when he isn't making comments as to how "un-acelike" their ace is). They seem to be comfortable around each other despite Asahi's obvious fear of his captain.
Daichi went to the same middle school as Ikejiri, and they were on the volleyball team together. Ikejiri was inspired by Daichi back then because despite the huge probability of their team losing, Daichi never gave up hope. Even now, nearly three years since they last saw each other, Ikejiri still remembers Daichi's quote, "We'll never win if we don't believe we can." Ikejiri used it in his match against Karasuno as motivation. After he lost, he approached Daichi and tearfully asked him to win for Tokonami.
Daichi notices his play style is very similar to Shōyō Hinata, so he thought he would be a worthy opponent for Hinata, but seeing how Takeru deals with Shunki Kawatabi and Kazuteru Akiu, he is convinced that they have very similar captaincy styles.
As a senior and captain, Daichi has developed better game sense and relationship with his juniors by Spring High Playoffs. Sometimes, even as an on-court coach, where Daichi can relay information to the team without Keishin saying anything, because he no longer needs to.