Bachou, also known by her true name Sui, is a central character whose life is dramatically shaped by the chaos of war in her homeland. She is the daughter of Batou, a powerful leader from the region of Ryoushuu. Her early life was spent fighting alongside her father in a coalition against the tyrant Toutaku. This period of her life came to a violent end when the warlord Sousou invaded Ryoushuu, an act that directly led to the death of Batou. Left without a home or family, Bachou was driven by a powerful desire for revenge, leading her to seek out and join the faction led by the protagonist, Kazuto, as a means to one day confront Sousou.

In terms of personality, Bachou presents a fascinating duality. On the surface, she is a classic tomboy, speaking and acting in a cool, laid-back, and often blunt manner. She is headstrong and prefers to solve problems with brute force and direct action rather than complex strategy, a trait she openly acknowledges. However, this tough exterior masks a deep-seated emotional fragility and a significant complex about her own femininity. She is extremely sensitive to romantic topics and can become incredibly flustered, stuttering heavily when teased or put into embarrassing situations. This is especially true in her interactions with Kazuto, who frequently teases her, causing her to erupt into classic tsundere behavior—lashing out and calling him a fool while hiding her true affections.

Her primary motivation throughout the story is a journey from vengeance to peace. Initially, her sole driving force is to avenge her father's death at the hands of Sousou. However, as she bonds with her new allies and experiences life beyond the battlefield, she gradually matures. She ultimately finds it within herself to reconcile with the past, forgive Sousou, and embrace a future dedicated to peace rather than retribution. Her role in the story is that of a powerful frontline warrior and a loyal friend. She is one of the first key members to join Kazuto's group, quickly forming an inseparable bond with the energetic fighter Chouhi. Their friendship is built on mutual trust and seamless cooperation in combat, where they are often seen launching enemies into the air together.

Bachou’s key relationships are central to her character arc. Her bond with Chouhi is one of her most defining features, as they become close friends and an unstoppable battlefield duo. Her relationship with Kazuto is more complex, beginning with her request for revenge and evolving through his persistent and teasing advances into a deep, albeit reluctantly admitted, love. Her development is marked by her moving from a state of vengeful solitude to becoming an integrated and emotionally open member of her found family.

Her notable abilities are firmly rooted in her upbringing as a warrior from Ryoushuu, a region famed for its cavalry. She is a master of the jumonji yari, a cross-shaped spear, and her combat style is defined by immense physical strength, blinding speed, and exceptional stamina. On the battlefield, she is a natural leader of cavalry charges, and her horsemanship is arguably the finest among the cast, reflecting her family's close ties to horses. In the anime adaptation, she possesses an additional unique insight, the ability to read an opponent's aura to gauge their strength and honesty. Outside of her martial prowess, she is known for a few comedic traits, including a famously large appetite she shares with a few other characters, eccentric training regimens like battling whirlpools, and being an incredibly heavy sleeper.