Gin is somewhat short, with pale skin, dark grey eyes, and long black hair. As a mafioso, she keeps her hair in a spiked bun, leaving sections of shoulder-length hair down. Most of it falls to the right side of her face, whilst a strand falls over the middle.
Gin wears a grey, short-sleeved v-neck, black trousers, and black heeled boots. Over her shirt, she wears a long, flared black coat is seen dressed in an outfit comprising of a long black cloak with a hood and frayed trim. The right sleeve, tightened by a black band on her bicep, is long with an extended part with frayed trim, and the left sleeve appears torn off, exposing her arm. She wears reddish-grey gloves that extend a tad beyond her elbows. The right glove being complete whilst the left glove is fingerless.
In addition, she also wears a black choker with a white cross on it, and a white mask that covers her nose and mouth.
Her casual wear is much less elaborate. She leaves her hair completely down, showing it to be silky and a bit wavy, falling past her waist. She wears a light, knee-length dress, black stockings, heels, and a stylish, buttoned coat. She also carries a purse with her. She is quite feminine in this attire, and she's noted as being exceptionally beautiful. 
As an assassin, Gin is silent and stealthy, described by Michizō Tachihara as being able to sneak behind someone and slash their throats in an instant. This was demonstrated when she snuck behind Ichiyō Higuchi and put a knife to her throat before she could notice. 
Fitting of an assassin, Gin is deathly quiet, seldom speaking, and pairs her silence with either indifferent or serious expressions. Similar to her brother, she's quick to lash out when provoked. Her fellow commander, Tachihara, has no problem antagonizing her, ending up as the target of her temper majority of the time. However, unlike her bother, her anger is often shortlived. Although she has a sense of humor, it's implied to be rather dry and sarcastic, such as writing "Congrats!" in the dirt to Tachihara when Atsushi Nakajima forces him to hold a baby during the Q Incident.
Hidden beneath her stoic personality, she blushes easily when embarrassed such as when Osamu Dazai mentioned how she was a "dainty little girl" when she was younger and when Higuchi saw her in her civilian clothes. She is also noted to have a very cute voice. When it comes to others, it appears she prefers keeping this side of her to herself and dislikes being put on the spot over it.  However, more recently, she has grown to become more comfortable with actually conversing with her coworkers and has also been shown to care about their wellbeing.
She is closest to Akutagawa, smiling fondly at him and returning home with him after her return from a mission. After Akutagawa promises to Atsushi Nakajima not to kill anyone for half a year, Gin notices Akutagawa's increasing irritability, attempting to find ways to pacify him, but knowing his demeanor leaves much to be desired in terms of relaxation.
Gin has no ability but makes up for it by having incredible physical skills. She is naturally gifted in stealth as she was undetected by the assailants who killed her friends in the slums and has been noted as having eyes that "absorb sound" and being "so quiet that [it was like] she had been painted into reality". She is agile and poised, capable of sneaking behind her targets undetected, making her a valuable assassin in the Port Mafia.
Compared to her older brother, she is more physically fit and capable of handling long-term strenuous activity.
She and her brother, Ryunosuke Akutagawa, were orphans and used to live in the slums along with about eight other kids. The other children happened to overhear a conversation regarding the time and location of a shipment the Port Mafia was supposed to deliver to subordinates. The men knew about this and sought out the children and mercilessly shot down everyone but Gin and Ryunosuke, who managed to escape thanks to Gin's quick-thinking, to death. Afterward, Gin tended to her brother's wounds, and after he woke up stated her reservations about him seeking out vengeance against their assailants only for him to go anyways to prove the value of their friends' lives. After Osamu Dazai extends an invitation to the Port Mafia to Akutagawa, Gin joins as well, however, the full circumstances behind her decision remain unknown. 
- The name Gin means "silver" (銀).
- Gin is a reference to Ryunosuke Akutagawa's work Ogin. The cross on her choker, while most likely aesthetic, could be interpreted as an allusion to the Christian themes found in Ogin.
- Gin's surname Akutagawa means "garbage, refuse, trash" (芥) (akuta) and "river, stream" (川) (kawa/gawa).
- The anime simplified Gin's design as her heels are instead boots and the cross is completely omitted.
- Harukawa often illustrates Gin with completely black eyes, harkening to Gin's hardened soul and her ruthless demeanor as a mafioso. However, her eyes soften somewhat when not at work.
- Harukawa has stated that Gin dresses the way she does at work to intentionally hide her true gender, but the reason for this has yet to be revealed. Despite this fact, she seems to become angry when someone (mainly Michizō Tachihara) openly misgenders her.
- Gin seems to find cats cute.