After surviving the entrance exams, Sakuta Azusagawa has finally enrolled in the same university as his girlfriend, Mai Sakurajima. He is gradually getting used to the unfamiliar environment as he attends student gatherings and makes new acquaintances. Everything seems to be going smoothly until Sakuta's friend and Sweet Bullet idol group member Uzuki Hirokawa begins acting out. With fellow Sweet Bullet member Nodoka Toyohama pleading for his help, Sakuta realizes that he has stumbled upon another case of the inexplicable Puberty Syndrome—Uzuki is feeling pressured by the sudden surge of popularity and rumors of a potential solo career. While Sakuta searches for a solution, another occurrence of Puberty Syndrome gradually emerges from the shadows.

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.

A great war occurred in the 20th century between humans and monsters. Since that time, the monsters rule the world in fear but keep relatively hidden from public view. A boy named Bokka ponders the past and wonders what became of the Meros Warriors who defended the world so bravely against the demons. He soon meets Kurofune and learns of the power of the Meros and the I-bar machines they ride in battle. Warriors are the only ones who can see and hear the Melody of Oblivion, a phantom girl hidden away waiting to be rescued and be the savior of mankind. During a battle between Kurofune and a demon, Bokka discovers something only his wildest dreams could possibly imagine...he too can hear that melody. Throughout his journeys, Bokka meets many monsters and their agents, friends, and companions as he discovers the true extent of his new powers. He must continue to battle evil in the hope of releasing Boukyaku no Senritsu and free a world that has forgotten its once beautiful melody.

Kai, a young middle schooler, lives in Hinashi Town, a lonely fishing village, with his father and his grandfather, a sun-umbrella maker. He used to live in Tokyo, but after his parents divorced he moved back to his parent's home town. Kai has trouble telling his parents the complicated feelings he has for them, and he's lonely and pessimistic about his school life. One of his joys is uploading songs he writes to the internet.

One day, his classmates Kunio and Yuuho invite him to join their band, "SEIRÈN." As he reluctantly follows them to Merfolk Island, their practice spot, they meet Lu, the mermaid girl. Lu sings merrily and dances innocently. As Kai begins to spend time with her, he starts to be able to say what it is that he's really thinking.

But since ancient times, the people of Hinashi Town have thought that mermaids brought disaster. Something happens that puts a huge rift between Lu and the townspeople. And then, the town is in danger. Will Kai's cry for the heart be able to save the town?

(Source: Fuji Creative Corporation)