DaiSuga

DaiSuga is the SLASH ship between Daichi Sawamura and Koshi Sugawara from the [https://shipping.fandom.com/wiki/Haikyu!! Haikyuu!!] fandom.

Canon
Daichi and Koshi are third years at Karasuno High School and are both in the vollyball team, Daichi is the Captain and a wing spiker and Koshi is the Vice-Captain and a setter. They have been friends since their first year. Daichi and Koshi hang out after school along with fellow third year and teammate Asahi Azumane.

Daichi stepped in as coach during their second year when their former coach Ukai was ill.

When deciding the team, Kageyama was chosen as the teams main setter, which upset Koshi. However Koshi said that he was relieved because he was unsure of himself and whether he made the right decition to give the ball to one person and not the other.

Fanon
Daichi and Koshi are seen as the parents of the boys vollyball team. Koshi is the kind and caring "mother" and Daichi is the also kind but can be scary if you make him angry "father". Since they are captain and vice-captain they are the some of the foundation of the team and because they are such close friends, it is understandable why they are shipped together.

Fandom
Daichi/Koshi on AO3

Trivia

 * Daichi Sawamura is the second biggest eater in the series.