Valentine's Day is coming up, and Yamada is still riding high on the fact that she got a kiss from Takashi Kosuda. However, Takeshita is starting to have second thoughts about helping her, considering her intentions. One day, after walking home with Mayu, Takeshita learns how Mayu's cooking puts hers to shame and how she really wants to confess her love to Kosuda, but Mayu is afraid that her clumsiness will drive him away. Despite this, Takeshita starts thinking that Kosuda deserves Mayu more than her friend Yamada, and this belief is reinforced when Yamada calls her out of the blue and asks Takeshita if she should do squats in preparation for sex.
Mayu makes a lovely chocolate cake and manages to work up the courage to walk over to Takashi's house and confess to him with the cake. However, Kazuki is the one who answers the door, foiling her plans. Elsewhere, Yamada is trying to make some homemade Valentine's Day chocolate, but many of her efforts end in failure or with something burning. When she finally makes something presentable, she tries to hand-deliver it to Kosuda's house, but wimps out and stuffs it in his mailbox anonymously.
The Kosuda family finds the box later, and Takashi is unsure of its quality or who sent it. Kazuki drops some bits of the chocolate in her fish tank, and the fish get violently ill. The next day, Kosuda tells Yamada about the chocolate he recieved, but the wording makes it sound like he completely ignored Mayu's gift by accident and thought the chocolate had a "unique" taste.
Some time after that, Yamada recieves a message from her erogami one night that her "sexual prowess" is falling, and that she needs to make up for it by doing something drastic. So after overhearing a couple of classmates mention it, she decides to go to school without any panties on. This leads to a few awkward moments, like nearly getting off in the classroom (until Takeshita verbally smacks her out of it) and trying to flash Kosuda when a faint breeze offers him a view of her uncovered crotch.