Ten years ago, at the peak of the VRMMO development industry, a game titled "Kiwame Quest" entered the scene with potential like no other. Boasting a colossal total of 10 sexdecillion branches of possible story scenarios, this game pursued ultimate realism, ranging from humanlike NPCs to the perfect replication of all senses and physical abilities. But it soon became apparent that the game was too realistic, and the popularity of VRMMOs in general gradually began to plunge. At present, due to an accident a few years prior, the high school student Hiroshi Yuuki now immerses himself in full-dive RPGs as a form of escapism. After failing to acquire the latest version of his favorite game, Hiroshi stumbles upon a game shop and meets its beautiful clerk Reona Kisaragi who convinces him to buy a copy of Kiwame Quest so that they can play together. The first time Hiroshi plays the game, he marvels at the realism it offers. However, his astonishment is short-lived as he sets off a series of misfortunes, quickly realizing that the game is even worse than his already stressful life. Nevertheless, Hiroshi still finds himself logging on again despite his growing contempt for the game. With no do-overs in his current disadvantageous situation, Hiroshi only has one goal—clearing the game!

As a young boy, Prince Oscar Lyeth Increatos Loz Farsas was cursed by the Witch of Silence, rendering it all but impossible for any woman to bear him a child. After 15 years of fruitlessly seeking a way to lift the spell, Oscar resorts to enlisting the help of a different witch. To this end, he heads to the Azure Tower, home of the Witch of the Azure Moon. Ascending the tower is no easy task; for decades, no one has overcome the array of traps, puzzles, and enemies designed to repulse any challengers. Oscar, however, easily climbs to the top, where he meets the fabled witch, Tinasha. To the prince's surprise, despite being hundreds of years old, Tinasha looks like a beautiful young woman in her late teens. Oscar explains his circumstances to the witch, who quickly perceives the true nature of his affliction. Though she claims that undoing the spell would be tremendously difficult, Tinasha proposes a workaround—to find Oscar a partner capable of withstanding the curse's effects. Realizing that such a woman is right in front of his eyes, Oscar boldly tells the witch to marry him. Though he is promptly rejected, the young prince refuses to back down, and the two eventually reach an agreement: Tinasha will leave the tower and live with Oscar for the next year. As the two continue searching for a way to lift Oscar's curse, word of Tinasha's emergence from isolation spreads, catching the attention of all sorts of old acquaintances.

The dawn of a decisive battle nears in Leyte Gulf against the Abyssal Fleet, the mysterious enemies that occupy the sea. As the only ones capable of fighting them, Kanmusu—young girls possessing the souls of warships—reorganize in preparation. The Shiratsuyu-class destroyer Shigure is assigned to the First Striking Force, Third Section—also known as 1YB3H. Unfortunately for Shigure, 1YB3H consists of the remaining few Kanmusu and serves as a diversionary fleet. Needing to confront the Abyssal Fleet head-on, it may well be their first and final mission together. Even so, Shigure refuses to let the enemy take another comrade from her. As they advance toward Leyte Gulf during this suicidal mission, the members of 1YB3H must support each other and persevere to prove their worth as competent ships.

Kimihiko Kimizuka has found himself inadvertently entangled in various crimes more times than he can remember, referring to himself as a magnet for trouble. One day, as if it was nothing out of the ordinary, a group of unknown men kidnaps him, forcing him to board a flight—where he also encounters a hijacking. Amid the resulting chaos, however, Kimizuka meets a stunning silver-haired beauty, going by the codename Siesta, who then saves the day. Claiming to be a legendary detective, Siesta enlists Kimizuka to be her sidekick. Though Kimizuka refuses at first, with Siesta's insistence, he eventually joins her—marking the start of a grand adventure spanning the entire world, preventing multiple threats that could spell doom for humanity along the way. Unfortunately, after three years of their unpredictable yet enjoyable time together, Siesta abruptly passes away. Distraught, Kimizuka tries to leave all memories of her behind, but as he begins to meet more people, it seems that Siesta's influence will never truly die.