Mitsuyoshi Yagyu, a 15-year-old third-year student at Daiwa Institute, bears the Pisces zodiac sign with a March 16 birthday. Standing 156 cm tall with measurements of 75-53-81 cm and blood type O, she is an A-Rank Toushi whose Three Kingdoms identity, "Mitsuyoshi 'Juubei' Yagyuu," marks her as heir to the legendary Yagyū Jūbei lineage.

Tasked by Himiko to gather Magatamas, she ventures into Kanto alongside Western warriors to test local fighters, though Himiko’s true motives elude her. Her past connection to Ekitoku from middle school fuels a later alliance. In her debut duel, she faces Shiryuu Chou-un with a self-imposed eyepatch handicap. When her blade shatters Chou-un’s inferior sword, she halts the battle, acknowledging his untapped potential and forging a rivalry tinged with respect.

A misplaced wallet forces her to seek Chou-un’s aid, leading her to join Seito. Partnering with Ekitoku against Inshun Hozoin, she endures poisoning during the clash, underscoring her audacity in perilous confrontations. Though confident in strategy, she concedes the lethality of battling Chou-un unrestrained, revealing acute self-awareness.

Trained at Daiwa Institute in swordsmanship, her upbringing and family remain private. Her shifting alliances and combat acumen position her as a pivotal tactician within the series’ conflicts, adapting seamlessly to evolving rivalries and loyalties.