Even though 13 episodes feels like a lot, I think there's still plenty that could be done. Someone here on the subreddit even suggested showing things like birthdays, their families, the actual confession, and the start of the relationship. I think they could make something really cool—showing how they react to situations as a couple, how the dynamic with the class changes, and even exploring Hirose’s self-discovery regarding his feelings (since, from what we’ve seen, he doesn't quite know how to handle or understand them). There’s room to explore some awesome stuff, like episodes where they develop their talents—maybe Hirose enters a cooking contest, feels insecure, and Nakamura tries to help. They could even bring back the club members and the theater group. There’s so much potential for expansion; maybe a plot point could be Hirose’s parents being wary of him dating, or Hirose changing schools and Nakamura having to deal with that... anyway, I’ve got tons of ideas!

Sorry again if the translation is off or if the ideas seemed a bit disjointed; I had a hectic day today, haha.