In the Taiheimeji era, the Tokugawa shogunate values breasts highly, equating them with wealth and status. The Manyu Clan, government allies, know secret techniques for breast enhancement, detailed in a scroll. Chifusa, the clan's heir, flees with this scroll, rebelling against the oppressive norms set by her clan.
In a world where large breasts are crucial, Chifusa Manyu, heir of the Manyu family, flees with their secret enlargement techniques. Attacked by her sister Kagefusa, Chifusa discovers her ability to transfer breast size and embarks on a journey with comrade Kaede.
Chifusa and Kaede, needing funds, encounter a landlady/Manyu assassin who tries to enslave them. Chifusa uses her Breast Flow technique to defeat her, gaining insights into this power and vowing to restore Kaede's breasts.
Starving, Chifusa and Kaede work at a maid bar, get fired, and help a man in a contest to appease a landlord. Chifusa wins despite Manyu attacks and impresses the landlord, who becomes infatuated with her.
Chifusa and Kaede turn divers to pay a food bill. Chifusa rescues Oiso from an octopus using her Breast Flow technique, which alters Oiso's breast size. Oiso then kills the octopus, thanking Chifusa.
Chifusa and Kaede save Osuzu from assault and help her win over Yasuke, a widower. They also deal with Yasuke's children, who miss their mother's breasts, promising them not to harass women after a unique deal.
Chifusa's enlarged breasts hinder her. At a temple, a nun links her powers to maternal longing. Kagefusa steals the Manyu scroll but can't use it. Moved by Chifusa's kindness, she returns it, promising to learn the Breast Flow technique.
In a village, Chifusa gets a massage for her painful breasts. She becomes a bodyguard to catch "The Boobie Kid," a thief. The thief, revealed as masseuse Momoha, imparts her breast technique to Chifusa before dying.
Chifusa and Kaede meet Lord Mie, now a commoner. They're attacked by a Manyu swordsman who kidnaps Chifusa. Rescued by Mie and Kaede, Chifusa defeats the swordsman. Mie refuses her gratitude gesture.
Chifusa and Kaede rescue painter Sakuji from Manyu guards. Misunderstandings arise between Chifusa and Kaede over modeling for Sakuji. After a confrontation with guards, Sakuji paints Kaede, deepening her bond with Chifusa.
Chifusa recalls using Breast Flow in a childhood duel with Ouka. As she and Kaede continue their journey, they realize Chifusa must return breasts to others she's affected.
In Chifusa's ancestral village, she learns her mother's sacrifice to protect the Breast Flow technique. She begins training to master it, only to face an attack by Manyu warriors led by Muneyuki and Ouka.
Chifusa, Kaede, and allies face Manyu assassins. Chifusa unlocks the Breast Flow by forming a maternal bond and escapes with Hazuki. They regroup with their allies, and Chifusa promises to continue her journey and restore what's been taken.
