Ayato Amagiri is the male protagonist of the light novel, manga, and anime series The Asterisk War: The Academy City on the Water. He is a sixteen-year-old student who transfers to Seidoukan Academy as a specially invited "tokutosei" student, a status arranged by the student council president using her authority. His primary reason for enrolling in the academy city of Rokka is to locate his older sister, Haruka Amagiri, who mysteriously disappeared five years prior. Haruka had also attended Seidoukan Academy before vanishing without a trace, leaving Ayato with few clues about her fate.

Personality-wise, Ayato presents a friendly, polite, and somewhat naive demeanor. He is inherently helpful, often extending his aid to others without considering the potential cost to himself, a trait that has led him into many complicated situations. Despite his gentle and modest exterior, he possesses an indomitable will and a deep-seated resolve to do what he believes is right. He can be shy and is notably oblivious to the romantic affections of the many girls who surround him, frequently finding himself in awkward or embarrassing predicaments, such as accidentally walking in on someone changing. Underneath his calm surface lies a勇猛 and刚正不阿 spirit, capable of fierce determination when protecting those he cares about.

Ayato's motivation evolves throughout the story. Initially, he arrives at the academy feeling adrift, unsure of what he wants to do with his life. This changes dramatically after he meets Julis-Alexia von Riessfeld, a princess from the autonomous nation of Lieseltania. Witnessing her relentless dedication to her ideals and her homeland inspires him. He begins to see his purpose as fighting alongside her and using his strength to protect her goals. Consequently, his personal quest to find his sister becomes intertwined with his desire to support Julis, especially as they enter the Festa tournaments together. His ultimate wish upon winning the Phoenix Festa is to discover Haruka's whereabouts, leading him to find her in a self-induced comatose state.

As a central figure in the narrative, Ayato is a student at Seidoukan Academy who quickly rises through the ranks. Despite a loss in his first official match against the then-number-one student, Kirin Toudou, he defeats her in a rematch to become the academy's top-ranked fighter, earning the alias "Murakumo" from Claudia Enfield. He partners with Julis to compete in the Phoenix Festa, a two-on-two tournament, and their victory sets off a chain of events that deepens his involvement in the mysteries of the city, including the shadowy organization known as the Golden Bough Alliance.

His key relationships are central to his development. His bond with Julis is the most significant; she is his primary partner in the Festas and the person he is most dedicated to protecting. Their relationship evolves from an awkward, confrontational start into a deep mutual trust and a formidable battle partnership. Saya Sasamiya is his childhood friend and former sparring partner, who harbors romantic feelings for him and provides steadfast support. Kirin Toudou, a younger prodigy, looks up to him as a mentor and also develops romantic feelings for him after he defends her from her abusive uncle. Claudia Enfield, the student council president, is a benefactor who brought him to the academy and is deeply in love with him, having foreseen him in prophetic dreams. His most crucial relationship is with his sister, Haruka. Her disappearance is the catalyst for his journey, and her actions in sealing his powers define his early struggles.

Ayato's character development is closely linked to overcoming the limitations placed upon him. Years before the story begins, his sister Haruka used her power as a Strega, a powerful witch, to place three seals on his vast and unstable prana, or星辰力. These seals were designed to unlock in stages as he matured. The first seal required him to find a purpose, the second required him to find trusted friends, and the third required him to surpass his sister in strength. Throughout the series, he breaks these seals one by one. Initially, breaking the first seal allows him to access his power for only a few minutes, causing him great pain afterward. Unlocking the second seal extends this limit to over an hour. By the time he prepares for the Gryps Festa, he finally shatters the third and final seal, gaining access to his full, unrestrained power.

In combat, Ayato is a master swordsman and martial artist who wields the ancient techniques of his family's style, Amagiri Shinmeiryu, or天雾辰明流. This style focuses on swordsmanship but also includes spear techniques, short sword skills, and grappling. He is a星脉世代, a Genestella, granting him enhanced physical abilities and the use of prana. He wields a powerful Orga Lux, a type of ancient weapon, known as Ser-Veresta, or the Black Furnace Magic Sword黑炉魔剑. This is one of the four legendary colored magic swords, a weapon that generates an intensely hot blade capable of melting anything it touches. The weapon has a demanding personality and a high prana cost, but Ayato achieves a high compatibility rate with it. A notable quirk of his fighting style is that he always calls out the name of his techniques, a habit he developed from a childhood promise with Saya. His notable techniques include "Twin Serpents," a cross-shaped slash, and "Nine-Fanged Blade," a series of incredibly fast slashes that can dismember an opponent.