This is a prequel to 'Don't Stay Gold', and appears also in the main manga 'Saezuru Tori wa Habatakanai'. It's from when Yashiro and Kageyama were back in high school.
This also appears in the main manga 'Saezuru Tori wa Habatakanai'.
Tadayoedo Shizumazu, Saredo Naki Mo Sezu