When Amane catches Eiji showing Nanako a beetle, she knows she’s gotta do something to get these two into a more age-appropriate relationship. Nanako still suggests they check out some fireflies at a pond, but Amane can work with that, and arranges another club field trip, using the nighttime setting to make it a test of courage that brings the two lovebirds closer together.
It works like an absolute charm—which is incidentally what Eiji and Nanako are full of—as Nanako naturally clings to Eiji when she gets scared, and he brings her even closer when he senses she’s in danger.
Unfortunately for Tao, she wasn’t let in on the plan for Koto to impersonate a ghost and grab her in the dark tunnel, but her real fear made it more likely Eiji and Nanako would run off together, which they do. When they get to the pond, there don’t seem to be any fireflies, so Nanako makes one with her phone, fooling Eiji with a giggle.
Then the fireflies do indeed appear, and the two get to share in another lovely experience together. When Eiji suggests they write senryuu to mark the occasion, she almost tells him how glad she is he’s there with her, but decides to be coy instead. Some things are better left unsaid…particularly when Eiji likely wouldn’t understand exactly what she meant!