When Tomoya walks in on Yukine masturbating, she decides to play a taste-test a game with him. In the second story, newlywed Nagisa wants a goodbye kiss from Tomoya. But Tomoya misunderstands the request.
In its original release, this doujin had a third story: a bad end for Kyou, which the comments here and elsewhere agreed was a tonal mismatch for the first two stories. This 2023 colorized decensored release with a new translation keeps things light and fluffy, so it omits this third story. (Maybe this further heightens the feeling of Kyou NTR.)
Decucking doujins is based and it's a win-win situation since cucks feel like they've been cheated out of complete release and get meta arousal from it.