These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
After Yuuji treats Kozue a bit too roughly during their first time, he begins avoiding her out of fear she'll be mad at him. When she finally corners him on the school roof top, she says she's not mad and then produces a copious amount of literature for Yuuji to read so they might have a better experience next time, including the Kama Sutra, Sex for Dummies, "an account of their encounter written in the style of a lusty romance novel", and numerous charts and graphs documenting present and future trends in their love making.
No shortage of others. Most of them involve Sumiyoshi.
Sumiyoshi: "No one knows more about Misaki than you do, Hiyama ... and vice-versa. Other than Misaki, the only person who knows as much about you is ... Yuuji, propably. Hiyama, you wanted Misaki to understand your feelings. But Misaki brushed you off. She's wrong there. But even if she does that, Hiyama, how could you turn your back on her? How could you not believe until the very end that she would understand. Isn't that what true friendship is all about?"
And after that Misaki and Kozue making up and Kozue informing Yuuji, that she is not afraid anymore to leave Japan as she knows her friends will always be there.
Genius Bonus: There are quizzes in-game with questions regarding classical Japanese literature and Mahjong. While there is no punishment for failing the first one, the second one is an important part of one of the routes. Alternatively, the Mahjong questions are a Luck-Based Mission.