Flighty, abrupt, and snappy with her elders, Jolyne in her teenage years was easily considered a delinquent and lost cause. Bitter at Jotaro for being absent from her life, she tried multiple times to catch her father's attention by committing multiple minor crimes and went to jail several times for them. Because of her father's absence, Jolyne was said to be dependent on the affection and approval of those around her, and she was ready to cover Romeo's accident, resulting in her being sentenced to 15 years in prison for it.
After acquiring her Stand and being told by Jotaro of his love for her, Jolyne noticeably matures, becoming more courageous and confident. "Reviving" Jotaro, who fell into a coma due to Whitesnake stealing his Stand and memory, turns into her first priority.
Jolyne retains her confrontational attitude throughout the story. A former delinquent living in a maximum security prison, Jolyne had to toughen up and can be especially rude. Her rare interactions with villains are either surly taunts or death threats, knowing how despicable most of them are. She also advocates aggressively asserting herself, especially in the prison, and once told F.F. to violently confront an inmate who cut in the queue for buying their lunch. Jolyne is particularly violent in her fights; she's used the cutting ability of her string to gruesomely wound her opponents, severing ears and nails for instance. Jolyne also has a vindictive side and repays tenfold any wrong committed against her, notably indirectly cutting Romeo's tongue for betraying her, moreover, Jolyne still holds a little grudge against Gwess, her first enemy and wants nothing to do with her despite the latter's effort to behave in front of Jolyne.
Jolyne possesses a fierce determination, carrying her through several battles and inspiring her companions. After learning of DIO's plan, Jolyne took pride in her lineage and opted to continue Jotaro's effort to seal the menace DIO left behind him. Jolyne stoically endures the hardships she faces and carry on her goal, disregarding the suffering and possible risks. Her determination is so great that she was willing to lose a limb or even her life to defeat her enemy and save her comrades, an inclination especially prevalent in her that culminated in her sacrifice to get Emporio away from Pucci. Even still, Jolyne once expressed her doubts about being able to stop Pucci after Weather Report's death and the priest's second escape.
Common in her lineage, Jolyne has honorable morals and treasures her family and friends. She would selflessly do everything in her power to help her companions and random victimized people, once helping a fellow mistreated prisoner to take back stolen money from her tormentors. Jolyne is willing to believe in the good in people, which resulted in a share of betrayals, but also earned her F.F.'s friendship. Jolyne is especially sweet to Emporio, her real first ally in Green Dolphin Street, and despite being an enemy, she didn't want to kill the Green Baby. Jolyne's primary motivation for investigating Whitesnake was her love for her father, and Pucci exploited that affection to escape her the first time.
Outside of combat, Jolyne behaves like an average young woman, if not a teenage girl, hanging out with her friends and occupying herself the best she can in the prison, as she is also fun-loving. Jolyne notably played ball with F.F. and Ermes, and made herself a navel ring while in isolation. Unlike her father, Jolyne is rather extrovert and easily expresses her feelings to others. She is a sociable woman, and can converse with her fellow prisoners easily, asking for explanation about the ins and outs of Green Dolphin Street.
Jolyne is notable for being somewhat libertine, being the first and only JoJo to admit to masturbating, and offhandedly commenting that snails' ability to copulate with anything makes her slightly jealous. Jolyne also mention her need to urinate in the middle of a fight with another person, a man at that. She is horribly embarrassed to talk about it in public and being caught in the act by a guard flustered and mortified her deeply.
Araki created Jolyne with the hopes of "making up" for his previous (and in his eyes, failed) attempt at a female protagonist. Aside from offering an interesting contrast to most shonen comics, he thinks she is a "real woman" sorely lacking in the medium. The role reversal between her and her father was devised for her character to go beyond the typical archetypes found in Japanese fiction.
- Jotaro Kujo: Her distant and near-fatherless childhood bore a tinge of loneliness in her, at times resenting him but also wanting his affection. Her relationship with Jotaro is challenging at first, not really fitting the typical father-daughter mold. When Jolyne was fourteen, she was wrongfully accused of pickpocketing. Panicked, she stole a car, sloppily tried to make an escape from the authorities, and was arrested soon afterward. Jolyne anticipated that Jotaro would pay her bail, but was sorely disappointed when she overheard her mother's frantic and unsuccessful pleas with him on the phone. Her father's absence following this led to her teenage years of delinquency (she later reflects that these events were a desperate call for attention). During Jolyne's imprisonment, Jotaro visited her in an effort to break her out. Angered that he would come out of the blue to see her after years of absence, Jolyne blew up at him, citing his inattentive behavior and his divorce. However, after risking life and limb to get Jolyne out as well as losing his Stand in the process Jolyne broke down and got Jotaro to safety, sacrificing her own freedom and vowing to get his Stand back. As time passed, Jolyne came to respect her father more and idolized him somewhat, adapting his trademark "Yare yare daze" into a more feminine "Yare yare dawa". When Jotaro returns later, both father and daughter show considerable care to one another, each in their own way.
- Mother: Jolyne's mother rarely appears and is hardly talked about. It's assumed that she loves Jolyne very much and dotes on her in Jotaro's absence, as she was the only known person to be allowed to call Jolyne "JoJo". It's mentioned that she is an Italian-American, making Jolyne 1/4 Japanese, 5/8 Italian, and 1/8 British.
- Holy Kujo: It is unknown if Jolyne has a relationship with her grandmother. However, she is shown at times to demonstrate the kindness Holy often did.
- Ermes Costello: Ermes is possibly the first true friend that Jolyne encounters in her life when they meet and bond in jail. Her relationship with Ermes resembles that of Jotaro's relationship with Jean Pierre Polnareff. Jolyne and Ermes see each other as worthy allies and friends, and because of their similar temper, get along well and kill time together. She has fought alongside Jolyne against many powerful enemies like Sports Max, Rikiel, & Donatello Versus.
- Emporio Alnino: Emporio's relationship with Jolyne is somewhat similar to her ancestor Jonathan Joestar to Poco, as Jolyne treats Emporio like a little brother and trustworthy ally, while Emporio is inspired by her courage and determination. Jolyne saves him from many dangerous situations and ends up giving her life so than he may live, trusting that Emporio will defeat Pucci. Emporio's relationship with Jolyne extends to Irene as well.
- Foo Fighters: Foo Fighters initially met Jolyne as enemies however, Jolyne spares Foo Fighters; grateful to Jolyne, it becomes an ally. Jolyne treats Foo Fighters with respect and is very friendly with her, and noting its naïveté, is protective toward it. Foo Fighters, nicknamed F.F. by Jolyne, is inspired by her determination, and cherishes the memories it has of her. It is ultimately willing to put itself in danger and even sacrifice itself to save Jolyne's life.
- Romeo Jisso: Before Jolyne's growth as a person, she and Romeo were in a relationship; with Jolyne being particularly affectionate and meek and Romeo trying to keep some distance, as he was suspicious of her past as a possible gang member. Their relationship ended when Romeo framed her for his manslaughter with aggravating circumstance, landing her in prison for a crime she didn't commit. After she escapes from prison, Jolyne pays him a visit and he weeps for forgiveness. Romeo shows genuine repentance and actually helps her, but while Jolyne doesn't show any lingering anger, she takes the occasion to damage his tongue to silence him.
- Weather Report: When they first met, Jolyne was flabbergasted by Weather's eccentric behavior. However, during the fight against Lang Rangler, both eventually see each other as allies, and trust each other. Anasui even suspects him to be a rival for Jolyne's love and is jealous when Jolyne is with him. Regardless, there are hints of Jolyne caring for Weather in a more-than-fraternal way notably when upon meeting again, Jolyne hugs Weather. Jolyne was also particularly distraught at Weather's death.
- Narciso Anasui: Though Anasui fell in love with Jolyne at first sight, the feeling wasn't mutual; Jolyne was not really sure what to think of him. He would sometimes try to seduce her in underhanded ways, such as asking F.F. to trip her down the stairs so he could romantically catch her or prompting a french kiss from a temporary-mute Jolyne. Even so, he's truly devoted to her and will do everything in his power to keep her from being distressed. He has risked his life for her on more than one occasion and turns murderous when Jolyne is severely hurt. At the end of Stone Ocean, Jolyne and Anasui's counterparts Irene and Annakiss want to marry each other.
- Enrico Pucci: Pucci only saw Jolyne as bait at first in order to get to Jotaro but as she proved to be a persistent thorn on his side threat while finding her father's Stand and memory disks, Pucci threaded carefully around her. Unaware of his involvement at first, Jolyne treated the priest with respect. They became enemies right away once she was informed that Whitesnake was Pucci's Stand and was eager to take his life. Jolyne became more then determined in stopping him and putting an end to his plans but her efforts would soon be fatal while she almost fell to Pucci's newly evolved C-Moon and would finally fall to his Made In Heaven while protecting Emporio, but has managed to cut the right side of his eye before dying.
- Donatello Versus: Due to his alliance with Pucci, Donatello and Jolyne were enemies. An additional reason for their antagonism would be that Jolyne's father destroyed Donatello's father. In the end Jolyne accidentally killed Donatello after being tricked by Whitesnake into thinking he was Pucci. Unbeknownst to either of them since Donatello was conceived when Dio possessed Jonathan's body Donatello is actually Jolyne's distant uncle.
- Johngalli A: As the man who got her framed for murder, Jolyne and Johngalli A were enemies. Johngalli A attempted to murder Jolyne and Jotaro to avenge DIO but failed. As payback, Jolyne pummeled Johngalli A as the sniper realized that Jolyne was more resourceful than she looked and inherited Jotaro's blood.
- Gwess: Jolyne's cellmate during her time at Green Dolphin. Jolyne inadvertently awakened Gwess's Stand power with her pendant. Gwess originally used her powers to bully Jolyne by shrinking her, but after Jolyne beat her she acted like her subordinate, advising Jolyne during her early days in prison and being somewhat afraid of her. Jolyne still had an arm-length relationship with Gwess but nonetheless tolerated her afterward.
- Miu Miu: Miu as an assassin sent by Pucci to make sure Jolyne doesn't interfere with his plans. Miu manipulated Jolyne into forgetting her goals and friends. After Jolyne remembered them, she beat up Miu and used her to escape the prison.