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…?”

When Purin sees Jobko through Serufu’s window, she heads over and gets introduced to the girl genius. The two end up hitting it off. Then, the next morning, Purin wakes to find Jobko in her room saying that she’ll be living there—effective immediately.

Kouki Kokoro, who says to call her Shii, suddenly drops in on the DIY club and asks if she can join. Everyone except Kurei happily accepts her. When Shii says she’ll be helpful because she’s stronger than anyone there, Kurei challenges her to prove it.

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!

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.