From a meta-perspective, episode 12. On the surface, it's a mostly standalone Hot Springs Episode that takes place after the main story, with a strange Hero of Another Story moment at the beginning adapting Eiichi's backstory. During the episode, the main cast spends a long time talking about the nature of Downloadable Content. They mention a few they find appealing in DLC: Keita likes seeing the hero and heroine interact in a low-stakes side story, Chiaki likes that a DLC epilogue can do weird things that could never happen in the main story, and both Keita and Uehara like swimsuit costumes for their favorite characters. In other words, by their definitions of DLC, episode 12 itself is DLC for the season.
With everyone's relationship status currently stable, the cast can hang out without the convoluted relationship drama of the main story.
Eiichi's backstory is a mini Bizarro Episode that doesn't fit the tone or content of the main narrative.
Most of the series has minimal Fanservice, but episode 12 has an extended scene of all the girls bathing in the hot springs.
