Sachiko Kojima (born 1969) was a Japanese student who went to high school in Kabukicho, Tokyo during the 1980s. During this time, she discovered the "burusera" business: selling used clothes to men for large sums of money. Kojima persuaded or even forced several girls from her school to enter this business under her eye; in return, she would be given a slice of their profits. One of the girls she forced, Mina Fukuhara, convinced ex-yakuza Kazuma Kiryu to intervene as she couldn't quit without becoming a social outcast.
Kiryu found Kojima amid a group of three burusera girls, relying on Fukuhara's information on her appearance. He told her to shut down her ring, Kojima wondering who told him about the business. Kiryu presented a few reasons as to why she should shut down the business, with one being that was unsanitary; she quickly countered it by saying she showers directly before using the underwear. He then asked her to think of her parents, which seemingly saddened Kojima as she was orphaned young and thus couldn't disappoint anyone with being a burusera girl; Kiryu was initially fooled by this, before she revealed that her parents were alive. Annoyed, he presented his final reason which was that she was playing with fire by using her sex as a tool to get money. Arrogantly, Kojima said that she hasn't been burned yet, but will let Kiryu know when she does.
Kiryu realized that she wasn't budging on her stance, proceeding to walk away. As soon as he did, he overheard a conversation between Kojima and an unsettling man named Shiro Kawakami. He became infatuated with Kojima and attempted to use a knife to kidnap her under the guise of love. Luckily for Kojima, the ex-yakuza Kazuma Kiryu was walking away from a conversation with her before hearing Tsukiyomi and Kojima's conversation and her cries of help. He immediately pushed over the off-balance Kawakami, getting between the two. Kiryu proceeded to beat down Kawakami, evading his knife strikes before punching him repeatedly, utilizing his brawling style. He immediately fled, afraid of Kiryu and what he might do to him.
Afterwards, Kojima asked Kiryu why he still helped her even after her arrogance. He responded that he wouldn't just let a teenager be assaulted, just as Fukuhara and her boyfriend Tat Miyoshi arrived to ask for Fukuhara's dismissal. Kojima relented, admitting that Kiryu was right and disbanding her burusera group.