Усаги и беспокойный день Святого Валентина

Valentine's Day will be here soon. Usagi desperately wants to give Mamoru her hand-made muffler but she's been moping about, concerned over the existence of [Mamoru's] girlfriend. Given Usagi's appearance, Makoto can't bear to tell her that the girl is actual Mamoru's fiancé. Soon after Usagi meets a first grade student- a girl named Hikari- who asks her for some love advice. Seeing her seriously go after the boy she likes, Usagi gains a little courage. Pushing each other on, the two of them go to select chocolates [for Valentines day], yet at that time they unexpectedly run into Mamoru and his girlfriend Hina. Hikari, surprised at seeing Hina, changes from her normal appearance. What could the unexpected relationship between Hikari and Hina be?