Thanks to Professor Yuuko Kouzuki's technology and Kasumi Yashiro's psychic powers, Cadet Takeru Shirogane travels back to his original world. With no time to lose, Takeru aims to enlist Yuuko's help in his world to complete the Alternative IV project—the last hope humanity has against the BETA, an alien species invading the planet. As the anti-BETA project nears completion, Takeru and other cadets graduate from the Yokohama pilot training academy. However, during a test of the new operating system for the Tactical Surface Fighters—the giant combat suits used by humanity against their adversary—the BETA ambush Takeru and his team. Barely escaping with his life, Takeru is left traumatized after witnessing the cruel death of one of his close friends. Losing his will to fight, Takeru flees back to the other world, where he experiences a similar tragedy. According to Yuuko's theory, people from parallel universes are bound to suffer the same fate. As a result, Takeru must overcome his trauma if he wants to protect the ones he holds dear.

Despite having a good reputation as one of the most seasoned guards in the local guild of Mebuki, Kikuru Madan believes he has been wasting his youth and hopes to spend the rest of it like any other person. However, his conscience prevents him from retiring at present, as he worries about the guild's future without him. Coincidentally—as if to help him find his successor—the guild's receptionist, Enome, assigns Kikuru four fresh recruits: the energetic beastwoman Hitamu "Hitamuki" Kyan, the prodigy Maidena Ange, the laid-back Toxico Dannar, and the stalwart Hanabata Nohkins. Although each of them possesses significant talents, they also display characteristics that detract from their potential—including Hitamu's extreme clumsiness and Hanabata's unintentional perverseness. As if there was not enough to deal with, the monsters outside Mebuki's walls start exhibiting odd behavior by targeting women salaciously, causing the party endless problems in more ways than one. Nevertheless, Kikuru is committed to retiring early; to achieve his goal, the guidance he gives the trainees will be absolutely essential.

While reminiscing about her journey so far, Aoi Yukimura finds herself eager to go mountaineering once more. A likely opportunity arises when Koharu Senjuin invites Aoi to check out the Mountaineering Club after school. As the head of the club, Koharu speaks enthusiastically of the activities she and the other members partake in, especially as they strive to reach the top in various competitions. Although impressed by the club's dedication to its goals, Aoi feels reluctant to join, preferring to learn and enjoy mountaineering at her own pace. Her experience during this brief visit, however, leaves her wondering why she climbs mountains in the first place. With the support of her friends, Aoi searches for the true motivation behind her hobby, all while continuing to train for the highly anticipated second trip to the summit of Mt. Fuji.

Akio Honjou is a high school student with a special gift for music. He can perfectly recall any piece of music that he has heard only once. One day, as he tries to reproduce a particularly soothing piano melody, he unexpectedly meets Juri Makina—the girl whose cell phone had spontaneously played the tune earlier in class. If art is the only way to truly know what landscapes populate others' inner worlds, then can this particular tune pave the way for Akio to begin to understand the more intellectual and emotional aspects of his captivating classmate, Juri?