Byaku is a fictional character from the anime and light novel series My Daughter Left the Nest and Returned an S-Rank Adventurer. In the story, Byaku is a young boy who serves as the escort and close companion to a mysterious girl named Charlotte, who is known for spreading the heretical teachings of Solomon.

Initially, Byaku and Charlotte are introduced as antagonists. They act as helpers to Count Malta, assisting him in his schemes against the noble House of Bordeaux. As part of this alliance, they participate in offensive actions, such as launching an assault on Bordeaux's defenses as part of Malta's undead horde attacks. However, the nature of their role in the narrative is not static. Later in the series, the dynamic shifts significantly. Byaku and Charlotte are referred to as former enemies when the S-Rank adventurer Angeline finds herself protecting them. Forces in the world seek to either manipulate Charlotte for her power or silence her entirely, placing Byaku in the position of needing to protect his charge and rely on the protection of others.

In terms of abilities, Byaku is a magic user. He and Charlotte begin training in magic together, though this training encounters a certain problem that becomes a point of focus in the story. His precise magical talents are not detailed in a simple list, but his role as an escort and his participation in combat and magical training indicate he possesses sufficient skill to act as a protector and combatant. Throughout his journey, his key relationship is with Charlotte, whom he accompanies faithfully. Over time, he also develops a significant relationship with the series' main protagonists, particularly Angeline, as the narrative shifts from them being enemies to her taking on a protective role over both him and Charlotte.