The stress in Saki and Nodoka's relationship has built up to the point where it's affecting their ability to play mahjong. In order to help them sort out their problems, Hisa makes them stay behind and gives them instructions for some special practice.
10 views Saki dj - Two Moons 1Series of Hibike! Euphonium doujins. 10 Volumes released as of Comiket 94.
61 views Hibike! Euphonium Kitauji Suibu Katsudou Nisshi Sono (Doujinshi) Ch. 3