The episode "Under the Moon" of Tonikaku Kawaii (Season 2, Episode 6) begins with Nasa and Tsukasa setting off on an onsen trip. Despite being legally married, both display an endearing awkwardness typical of early dating phases. The excitement for the trip, marked by Nasa's amusingly exaggerated reactions to Tsukasa's yukata, sets a comedic tone for the episode.

The couple arrives in Kusatsu, a place famous for its historic hot springs. Nasa, unfamiliar with local traditions, is surprised to learn about onsen salts from Tsukasa, adding a humorous twist to his usually knowledgeable character. Although there is an expected hint at Tsukasa's mysterious past when Nasa asks about Kusatsu's age, Tsukasa simply reads from a historical plaque, shifting the focus back to their shared experience.

The main event of the episode is their open-air bath together. Nasa, struggling with his nerves, eventually musters the courage to ask Tsukasa if she wants to bathe with him, and she agrees. As they relax in the tub under the moonlight, they exchange affectionate words. Nasa expresses his love for Tsukasa, followed by Tsukasa's somewhat indirect confession of her feelings, using Natsume Soseki's poetic phrase: "The moon is beautiful," a cultural euphemism for "I love you."