Lamune tells the story of a boy named Kenji and his childhood friend Nanami. Although, everyone seems to know that they have a relationship, neither are determined to push it anymore than close friends. The story goes through flashbacks, explaining why they are such close friends and any action doesn't seem to push them apart, but draw them closer. (Source: ANN)

The docks provide a look into the very essence of ocean life—the calm, rhythmic sounds of the waves, the small bugs skittering across the pier, and—mermaids!? Takurou Mukoujima's quiet days spent fishing are no more when he reels in the energetic mermaid Muromi-san, who proceeds to entertain herself around her newfound friend, even if he is obviously disinterested. Now with a talkative and reckless companion always by his side, Takurou struggles to avoid getting caught up in Muromi-san's pace as she starts to invite her deep-sea friends, making the dock a popular gathering place for mythological creatures. Every day might be new and exciting, but all Takurou really wants is to fish in peace!

Having fulfilled their destiny during the events of Yuuki Yuuna wa Yuusha de Aru, Sanshu Middle School's Hero Club—consisting of Yuuna Yuuki, Karin Miyoshi, and siblings Fuu and Itsuki Inubouzaki—is back in full swing, helping out those in need wherever they can. They have also gained a new member, a hero from the past named Sonoko Nogi. But eventually they notice that someone who should be among them, Mimori Tougou, is missing; any trace of her existence is completely gone, save for the girls' memories. With no leads on Tougou's whereabouts, the girls regain the ability to transform and begin the desperate search for their lost friend. But what they find is more shocking than any of them could ever have imagined, and the consequences of their actions begin to change life as they know it.

Since childhood, 15-year-old Umika Konohoshi has been fascinated by aliens, hoping to one day voyage to outer space and befriend them. Unfortunately, this fixation has caused her peers to label her as odd, intensifying her struggle with severe social anxiety. Nevertheless, Umika's passion for the extraterrestrial persists, and she deeply believes that her true purpose is outside the confines of Earth. On her first day of high school, Umika's wish of meeting an alien seems to have finally come true when she encounters Yuu Akeuchi—a classmate who claims to have crash-landed on Earth with no recollections of her past. Umika tries to seize this opportunity to make friends with Yuu, but her lack of confidence hinders her. Sensing Umika's distress, Yuu suddenly uses a strange power to delve deep into her mind, thus sparking a friendship that may just help Umika reach her dreams.