The DIY club needs more members to stay open. As Serufu wonders just how to do that, her classmate Hikage Takumi offers a thought—“If you made the club room cuter, then maybe other students would take an interest…?”

A genius exchange student from America has surprisingly enrolled at Gata Girl’s instead of YuuVoc. One day, Serufu and the others find her sobbing behind the club room. When she finds out that they’re the DIY club, she starts badmouthing DIY.

The DIY club’s tree house plan is moving ahead. The items they made are selling, so they’ll soon have the money they need. With the club’s input, Serufu draws concept art to base the blueprints on, but no one has drafted anything this big before!

Midterms are over. The parts for the secret hideout have been ordered. Kurei has announced that they’ll start building on Monday. Serufu asks everyone to come to her house on Sunday, before building starts, so that she can show them something.

Finally, construction on the secret hideout begins! When Serufu invites Purin to build it with them, Purin’s secret is revealed. Together, the club members work through rainy days and sunny ones while their summer vacation deadline draws nearer.