They agree to a "nerd ban." Every time someone mentions something otaku-related, they must put money into a penalty piggy bank .

If you are looking for (often referred to as "paper" in shorthand) for this specific episode, the most popular scenes include:

Hirotaka holding the piggy bank with a pouting face.

By sheer coincidence, their coworkers Hanako and Kabakura are also at the park. This leads to a hilarious mix-up during a horror ride where the couples accidentally swap partners in the dark.