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 decides to go to the beach. They’ll gather materials to make little things like bracelets to sell, adding to their club funds. When Purin hears that Jobko is going to the beach, she decides to go along, unaware that it’s a DIY club activity.

The heat and humidity of the rainy season make it difficult for the DIY club to get any work done, so Kurei invites everyone to her house for air conditioning. When Serufu and the others visit Kurei’s room, they discover a surprising side to her.

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.

The DIY club suffers a massive shock. Devastated, they head home without beginning the construction of their secret hideout. When Purin hears what happened from Jobko, she digs out an old keepsake and goes to see Serufu.

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.

The DIY club holds a celebration at their newly completed secret hideout. Then summer vacation starts and Jobko heads home, promising she’ll see everyone again. Purin takes Serufu to the DIY club, saying that the secret base is still missing something.