Senju Kawaragi/Synopsis

Background
Senju is the youngest among the Akashi children collectively known as the "Mysterious Three Siblings.” Her eldest brother Takeomi Akashi is a founding member and the former Vice President of the First Generation Black Dragon before joining Brahman, while her second eldest brother Haruchiyo Sanzu is the former Fifth Division Vice-Captain of the now-disbanded Tokyo Manji Gang. Currently, Haruchiyo is a trusted member of the Kanto Manji Gang under the leadership of Manjiro Sano as a result of his disinterest in Senju and Brahman as a whole. Despite Takeomi’s endorsements, Haruchiyo is known to be detached from his siblings and their family business.

Senju 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, are currently 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 the city'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 is 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. 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, Takemichi envisions a future where Senju is fatally wounded on the ground after making contact with the stick, 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 ring. The company executive offers her gang a partnership to which she is forced to accept, but not after condemning their business' unlawful ways of drawing in commoners to participate in illegal schemes. Takeomi is galled, then remarks her behavior toward a valuable customer along with her flawed decision-making, orienting Senju to ward off any personal sentiment from influencing her work decisions and measures. He points out that for this reason, Mikey succeeds in leading his gang.

Later that evening, Senju institutes 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. 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. Additionally, 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 Tokyo.

Afterward, Senju leads Takemichi to a Tanzaku where they wish for the triumph of their aspirations. She promises to protect Takemichi and asks him to be friends. They share a handshake, but she unknowingly triggers a much more lucid vision in Takemichi's eyes 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. Instead, he is cornered by four of Rokuhara Tandai's men who ought to kill him; as one of them unsheathes a gun, Senju comes running back to protect him. However, she is swept off her feet by Takemichi and neither of them is hit. Their killers are enraged and fire another round, but they are eventually scared off by Draken who arrives at the amusement park just in time for the attack. He blocks them both from the bullets and soon collapses as his gunshot wounds become lethal. Senju calls an ambulance, but Draken dies before he can be taken to a hospital. The aftermath of Draken's death causes Brahman to arrive at the amusement park with an angry Takeomi in the lead. As her gang members gather, he seeks revenge on Rokuhara Tandai despite Senju's refusal on starting an immediate battle without much preparation. The fight begins upon the Three Deities' arrivals. She pleads Takeomi to stop the fight but is eventually told by Wakasa Imaushi to not get herself involved before running off with Benkei to take South down. She is forced to watch from the sidelines with Takemichi until Brahman slowly loses against the two gangs, coaching her to take control. As she faces South, Takeomi begs her to let the Brahman executives handle the fight instead, commenting on her subservient fighting abilities against her opponent. Senju does not listen and overpowers South; her determination to bring Brahman to victory awakens the potential she has kept hidden from Takeomi to not lead him astray from a righteous path in life.

She fights South, then pronounces herself as Brahman's true boss. Marveled, Takeomi reminisces the day when Senju proposed to build a team with the First Generation Black Dragon members. She stated how she wanted to defeat Mikey from the disbanded Toman and offered Takeomi to be her advisor. The memory guilts him; he pins the blame on himself for restraining Senju's potential and causing Draken's death, but she shoulders the blame due to her overall ineptitude as Brahman's leader. To repay her shortcomings, Senju now believes that she has to take South down.

The two continue to fight, but South knocks Senju off and she is defeated. Replacing her in the battle is Mikey, who previously beats Kakucho and encourages South to fight him. Senju opposes his decision and tells him to move out of the way, claiming South as her opponent and not his, but Mikey threatens her to not interfere in their battle with a glare. Out of fear, Senju submits to his orders and watches them fight.