Gin Akutagawa/Synopsis

Armed Detective Agency vs. Port Mafia Arc
Gin makes her entrance meeting up with Tachihaara and Hirotsu, arriving from the darkness in her silent manner. Tachihara insults her, calling her a "freak". Gin lashes out, putting her knife to Tachihara's throat. In return, Tachihara presses the muzzle of his gun against Gin. Hirotsu threatens to use his ability on them if they do not stop, and Gin coolly backs down under his threat.

With Black Lizard united, Higuchi gives them the order to kill the Armed Detective Agency. The squadron easily enters the building the Agency's located in, attempting a surprise attack as part of the Port Mafia's effort on chasing down Atsushi Nakajima, to hand over to the Guild in exchange for a massive reward. However, Black Lizard is overpowered, and Gin is defeated by Kenji.

She later makes her move alongside Black Lizard confronting Higuchi after Akutagawa's defeat by Atsushi. She sneaks behind Higuchi, demonstrating she could easily slit Higuchi's throat if she had to. Despite Akutagawa's grave injuries, Gin and the others question Higuchi's judgment, trying to act without receiving orders. However, despite her cold front, she arrives to assist Higuchi in saving Akutagawa from a rival group attempting to get revenge against the Port Mafia. Given her participation, Gin shows her respect for Higuchi's drive. During Akutagawa and Higuchi's reunion, Gin stands outside the room, seeming to nod in approval.

The Guild Arc
It's implied Black Lizard assisted in killing an assassin sent by the Guild alongside Motojirō Kajii and Chūya Nakahara. When Port Mafia's boss makes his entrance, Gin promptly shows her respect.

During the three-way war between the Port Mafia, the Armed Detective Agency, and The Guild, Gin attempts to monitor Dazai and Atsushi's movements, following Dazai when he starts walking away. Dazai's noticed her the entire time and asks her to reveal herself. Shocked Dazai noticed her, Gin instinctively lashes out, drawing her knife to Dazai's neck. She demonstrates an understanding of Dazai's reputation when calmly putting her away at his request, staying out of his and Higuchi's meeting over the released Q, acting as "guards" to Dazai

It isn't until Dazai brings up how she used to be much shorter and cuter when first in the mafia, revealing she's a girl. His comment catches Gin off guard, and she looks away, asking him not to change the subject.

After Q's kidnapping by the Guild, Black Lizard participates in defending their territory from further damage of Dogra Magra's widespread mania.

Later, during Ōgai Mori and Yukichi Fukuzawa's secret meeting, she—along with the other Black Lizard leaders—act as the boss's escort detail. The group did not hesitate to try attacking Fukuzawa when tensions overflowed, only to be deceived by Tanizaki's Light Snow ability.

The Guild Aftermath Arc
After a long-term absence during the three-way conflict, Gin returns after being absent on a mission during the incident. She is seen by Katai in her civilian attire, and Katai sees her as a beautiful young woman he falls in love on first sight. The next time she is seen is by Higuchi, who spots her smiling fondly at Akutagawa, mistaking her as Akutagawa's lover.

Pursued by Katai (along with Atsushi Nakajima and Doppo Kunikida) and Higuchi, Gin attempts to run away. However, she is forced to speak to them when they catch up to her. She explains she asked Akutagawa, revealed as her older brother, to take care of her work clothes after they were done in at a laundromat.

Her appearance and relation to Akutagawa shock the group, leaving her further exasperated. When Katai finally tries to develop a relationship with her, Gin promptly shuts him down. Later, Gin is asked by Higuchi to call her "older sister" as her superior.

Cannibalism Arc
With the arrival of the "masked assassin", Black Lizard gets assigned to scoping out and raiding his hideout. However, their target already fled the scene. This failure leads to Fyodor Dostoyevsky's "cannibalism" scheme. Assigned to "siege duty" during the raid on the Agency, Gin and the rest of the mafia's most prominent Mafiosi move in to kill Fukuzawa to save Mori's life. The group nearly ends in a massive face-off against the Agency, only to be deceived by Tanizaki's Light Snow once more. Black Lizard apprehends him and holds him hostage.

Gin stands behind Tanizaki, with Hirotsu warning Tanizaki that if he doesn't cooperate with the interrogation, Gin will kill Naomi Tanizaki. Naturally, this enrages Tanizaki. His violent mood swings unsettle Gin. The situation escalates, and Tanizaki escapes just as Tachihara tries to shoot him. Light Snow nearly gets Gin killed, until Hirotsu warns Tachihara he might shoot an ally. Gin hears the door lock, barely evading Tanizaki trying to kill her from behind. Hirotsu comes to Gin's aid, but Tanizaki escapes.

After Alexander Pushkin's defeat and Mori's recovery, Gin accompanies the combined forces of the Agency and Port Mafia to confront him.

Decay of Angels Arc
With Black Lizard assigned to the Agency's protection after they are framed for several accounts of murder, Gin holds her peace on the subject, leaving Hirotsu and Tachihara to argue over whether or not it's worth the trouble of protecting them when Yosano and the others leave a hidden base against Mori's instructions. She watches in shock as Kenji Miyazawa takes the bait of a car that explodes, mistaking it for Atsushi's.

Government agents attack the group, with Black Lizard protecting Tanizaki and Yosano whilst they help Kenji. The assault leads to the appearance of a mysterious, hooded figure with the ability to manipulate metal. With the drastic turn, Black Lizard and the others make a retreat. Gin remains silent throughout the whole discussion. The figure tracks Yosano down, revealing the dog tag of the soldier she befriended. In her shock, she's nearly killed, but Gin comes to her rescue, sustaining a gash on her arm. Tachihara later comes to her aid.

After their escape, Gin keeps a hand on her injury, assuring Yosano that the door, rigged with explosives, will keep them safe. Doubtful, Yosano tells them to escape on the boat without her. She listens in on Tachihara's conversation with Yosano, suddenly walking towards him. She only speaks his name before stabbing him in the stomach. She shouts that her blade is moving on its own, forcing her to stab Tachihara and try attacking Yosano. When she fails, she's forced to stab herself, collapsing while the knife floats away.

It is later revealed through Tachihara's flashback that Gin and Hirotsu had survived his attack against them and had ended up being treated in the hospital for their injuries and he had gone to visit them. As Hirotsu greets Tachihara and expresses relief that he is alright and had "survived" with only light injuries, Tachihara experiences intense feelings of discomfort from his comments. Gin notes the light nature of all of their injuries to which Hirotsu agrees, stating the attack only seemed like a mere "performance". As Tachihara laughs in response to his comments and tries to leave the room due to having "another job" to do, Gin expresses curiosity about what he means. After Tachihara thinks about his status as a Hunting Dog and asks Hirotsu if he is suited for the Mafia.

Gin looks to Hirotsu in awe and begins laughing with him as Tachihara looks to them with a sorrowful look. Hirotsu expresses to Tachihara that he is a "Mafia among the Mafia" and a person with qualities that are befitting of one (i.e. recklessness, bravery, and hot bloodedness) as an example that everyone should look to which Gin agrees in her silence. When Tachihara asks Hirotsu what he thinks about the Detective Agency and their innocence, Hirotsu looks to him in amazement and notes he must be more injured than they were to not know the answer. When Hirotsu says anyone in the Mafia would know the answer and turns to Gin for her opinion, she answers back that there is no question that the Detective Agency is innocent as it is impossible for them to ever be terrorists.

Later on, after Akutagawa is turned through Bram Stoker's infection-type ability and infects Higuchi, the latter attends a mafia meeting and bites Gin, turning her into her kind. Hirotsu tries to attack Higuchi, only for the latter to immediately overpower him with her strength. In turn, Gin bites Hirotsu and turns him to their kind, instructing Tachihara to escape immediately.