Six months before the opening of the patisserie La Soleil, Chocola and Vanilla are still kittens trying to fit into the Minazuki household. As the two youngest catgirls under Kashou and Shigure's care, the two learn from and mature alongside four other catgirls⁠—Azuki, Maple, Cinnamon, and Coconut⁠⁠. Soon, they approach their first Christmas together as a family.

A college student and his friends—Seitarou Higuchi, Akashi, Ozu, and Ryouko Hanuki—share various stories about a submarine that can travel through land, each one trying to outdo the others in terms of creativity. Ranging from a journey to stop the melting of the ice caps, to a quest to stop perverts from spying on girls, and to a fishing trip, no topic is off-limits.

Spring has finally arrived in Moomin Valley, giving way to another great adventure for Moomintroll and the rest of its inhabitants. With Snufkin coming home from his winter migration, the locals of the valley finally begin to rise from their hibernation. Finding a mysterious hat, the Moomins cannot bring themselves to throw it away due to its fine quality, instead hoping to eventually find its owner. While playing games with his friends, Moomin tries to hide in the silk hat. When his friends come looking for him, they are shocked to discover that Moomin has transformed into a hideous creature. Examining himself in the mirror, he is disgusted to find himself completely unrecognizable. Transforming back to normal after scaring his friends and family, Moomin and Snufkin decide to toss the hat in the river. As it drifts away, they begin to wonder who the hat belonged to and whether its owner will return for their lost possession.

Far from the city's noise lies Torishirojima—a quaint and peaceful island where time seems to move slowly. Hairi Takahara, a young boy nursing a wounded heart, uses the recent death of his grandmother as a quiet reason to leave the city for a summer retreat to Torishirojima. Upon reaching the island, Hairi finds himself surrounded by a refreshing, laid-back atmosphere, a far cry from the hustle and bustle he is used to. After moving in with his aunt, Kyouko Misaki, he prepares to spend the summer helping her sort through a shed full of artifacts his grandmother collected over the years alongside his cousin, Umi Katou, who is staying with them. While adjusting to the island's slower pace, Hairi decides to spend his free time exploring. He soon meets the cheerful Tsumugi Wenders; the antisocial Shiroha Naruse; the wandering Kamome Kushima; and the sharp-tongued Ao Sorakado. Drawn into their lives and the island's subtle mysteries, Hairi is gradually swept up in a summer filled with fun, nostalgia, and life-changing moments that will stay with him forever.