Senju Kawaragi/Synopsis

History
Senju is the youngest among the Akashi children collectively known as the "Mysterious 3 Siblings.” Her eldest brother Takeomi Akashi was a founding member and Vice President of the First Generation Black Dragon before joining Brahman, while her second eldest brother Sanzu was the former Vice-Captain of the Fifth Division in the Tokyo Manji Gang. Currently, Sanzu is a trusted member of the Kanto Manji Gang under the leadership of Manjiro Sano.

While not much information is given about her family, Senju prides herself on having a close relationship with Takeomi. On the other hand, Sanzu finds no interest in her and Brahman despite Takeomi’s endorsements. During a day-off shopping spree with Takemichi Hanagaki, she mentions how Sanzu's detachment from his siblings is what led him to join Kanto Manji.

She uses a fictitious surname “Kawaragi” instead of her factual surname to stay professional in the workplace. However, her true reasons for doing so, as well as her family history, remain unknown.

Three Deities Arc
As Takemichi Hanagaki travels back to the year 2008, Senju appears along with other notable members of the delinquent gangs Brahman, Rokuhara Tandai, and the Kanto Manji Gang who all concurrently control Tokyo as a result of Tokyo's two-year Sengoku Period. She is soon addressed by Kazushi Yamagishi as a charismatic leader of the infamous Brahman, a formidable gang that excels in working in the shadows, and recognized as the current ruler of Shinjuku. On a rainy evening in Tokyo, Brahman clashes with Rokuhara Tandai to recruit Takemichi into their gangs. Senju watches the confrontation from the sidelines, avoiding the spotlight as Takeomi Akashi leads Brahman in her stead, but eventually performs a surprise attack on Rokuhara Tandai's Representative South Terano in hopes of taking him down. She forcefully thumps his head and faces him, but Shion Madarame comes to threaten her. To her luck, she is protected by Keizo Arashi who knocks Shion out. He reminds her that their current goal is to recruit Takemichi rather than to brawl, but Senju tells him off before he gets attacked by Kakucho Hitto. She watches the fight between the gang leaders unfold, until South recovers from her attack and proposes to settle the dispute between them through a one-on-one fight. Senju rejects his offer, adamant in only recruiting Takemichi. Cops arrive as their confrontation causes traffic. Senju leaves with Brahman after acknowledging Takemichi's willpower, then meets him again at D&D Motors where Ken Ryuguji warns Takeomi to not drag former Tokyo Manji Gang members into Brahman's plans. Senju explains to a confused Takemichi that the gang's goals align with Draken's to dissolve the Kanto Manji Gang and rescue Manjiro Sano from his dark impulses and asks him to join Brahman herself. Draken refuses, but Takemichi accepts. Once he is welcomed into Brahman, Senju makes Takemichi her gofer and tells him to meet her the next day at three in the afternoon in Harajuku. As they meet, Takemichi is surprised to find out that she is apparently a girl.

In Harajuku, Senju drags Takemichi around from store to store to shop for clothes. He makes small talk and asks her about Brahman and her relationship with Takeomi who she admits to be her older brother, then tells him that the surname "Kawaragi" is merely fictitious, a name she uses for the sake of professionalism. Having admitted that her real name is "Senju Akashi," she mentions Toman's former Fifth Division Vice-Captain Haruchiyo Sanzu and claims that he is her second older brother. Allegedly, his disinterest in Senju and Brahman as a whole is what led him to join the Kanto Manji Gang rather than theirs, serving Mikey as his trusted second-in-command despite Senju's unbelievable strength and power. The two continue their shopping trip and eventually head out to eat ice cream. Once done, Senju bids Takemichi farewell and throws him her finished ice cream stick, sealing a promise to go out on another food trip some other time. However, once he touches the stick, Takemichi envisions a future where Senju is fatally wounded on the ground, murmuring joyfully through tears that he has "kept his promise."

A few days later, Senju attends a meeting with Takeomi to discuss matters about Brahman's involvement in a prostitution company's collaboration offer. She is forced to agree, but condemns their business' illegal and unclean ways nonetheless. Takeomi tells her to treat their customers properly and warns to not let her personal emotions affect her decision-making, and that her emotions as a child is what distinguishes her from Mikey.

Later that evening, Senju holds a meeting with all Brahman members in their hideout. She formally introduces Takemichi as the gang's newest member and hands him his very own uniform, then announces a declaration of war against Rokuhara Tandai and the Kanto Manji Gang nicknamed as the Battle of Three Deities on the 14th of July. As Brahman erupts in cheers, the meeting ends.

After the meeting, Senju invites Takemichi to an amusement park where they discuss gang matters while out on the rides. She tells Takemichi that she and Takeomi will manage the battle between Brahman and Rokuhara Tandai, while he and Draken are in charge of taking Mikey down with his gang. She says that Takeomi's objectives in leading Brahman has changed; rather than to make the gang stronger, he wishes to expand its population and involve more people in their business, hence the need to settle the score between the Three Deities first before Brahman can be proclaimed as the one and only ruler of the Kanto region. Afterward, Senju leads Takemichi to a Tanzaku where they both cite down their current goals and wishes. She promises to protect Takemichi and asks him to be friends, sharing a handshake with him right after, but once again unknowingly triggers a vision, this time much clearer, where she is helplessly wounded and at the brink of death. A sudden downpour prompts her to seek shelter at a nearby food stall, then later on excuses herself to use the restroom. Takemichi lets her be, but soon realizes that Senju is more prone to the dangerous fate he has been envisioning now that she is out at the park alone. Alarmed, he makes it his goal to find her but to no avail as he is cornered by four of Rokuhara Tandai's goons who apparently ought to kill him.