Ermes Costello

Hermes Costello (エルメェス・コステロ Erumeesu Kosutero) is a protagonist featured in Part VI: Stone Ocean and one of Jolyne Cujoh's greatest allies.

Personality
Despite her tough exterior, Hermes is very proud, loyal, and headstrong. She does not shy away from a fight and is willing to do just about anything to put herself in a better situation whether it is taking a bet that could risk her organs to even offering her panties.

Hermes shows a severe sense of resilience for she was still on her feet and moving around even after Marilyn Manson took her liver and survived the shared experiences of suicide attempts from McQueen. She has a good sense of justice but violently punishes anybody who crosses her way.

History
When Hermes was seventeen, her older sister allowed herself to be spotted by a homicidal car salesmen named Sports Max, saving Hermes from his wrath but ending her life in the process. Meanwhile, Sports Max, though caught and arrested by the police, was not tried for the murder and was instead sent to prison for tax evasion. Enraged, Hermes purposely had herself thrown in jail, intending to track Sports Max down. Her crime was armed robbery and it was not her first offense; her sentence was to be 8 years.

Stone Ocean
She first met Jolyne Cujoh when they were held in momentary captivity next to each other. Annoyed by Jolyne constantly banging her head due to her humiliation earlier that day, she yelled at her to pipe down. She was amazed to hear Jolyne confess her innocence to her crime and admired her honesty. On their way to Green Dolphin Street Prison, Hermes warned Jolyne to get her hands on cash, as bribery was the quickest way to escape "prison life". In return, Jolyne saved Hermes from a brutal beating using Stone Free. Although not cell mates, the two have remained somewhat close to each other ever since.

While in prison, Hermes used money as a medium so when the janitor, Xander McQueen, stole her money, she pursued him after being in the infirmary six times for a fever. Once she encountered the janitor, she learned that he was severely suicidal and due to Highway to Hell, she was forced to encounter similar experiences whenever he attempted it. While she saved him from the attempts on multiple occasions (even offering him her panties as a way to cheer him up), he still found means to kill himself but not before she split his skull using Kiss, resulting in McQueen's death while saving her own.

She later volunteers as part of a search group with Jolyne and four others in order to find two lost inmates. In their search, they encounter Whitesnake's stash of isolated stand discs and Foo Fighters, who was designated to protect the discs. After a hard fought battle, F.F. was liberated of its duties and pledged allegiance to the two.

The following days included an encounter with the gambler Mirashon who bet on a game of catch (that Jolyne and  Foo Fighters couldn't relay the ball one hundred times). Hermes persuades Jolyne to agree to the bet (which she won) before Mirashon made another bet for more money. The new bet enticed Costello to not only agree but to put herself into the bet so she could get the thousand dollars. Costello lost the bet and found herself at the mercy of Mirashon's stand, Marilyn Manson, who took her gold tooth, money from her surgically repaired breasts, and her liver. Jolyne eventually wins the liver and money back from Mirashon.

She remained in intensive medical care after her battle with Sports Max and does not appear again until Jolyne escapes from prison. She was one of the final members in the last battle against Enrico Pucci, and dies in the struggle.

After Emporio Alniño manages to defeat and kill Pucci, Hermes's alternate universe counterpart is seen being ejected from a bus for attempting to pay with a fifty dollar bill. The counterpart feels infuriated and even wonders if the bus driver mistook her for an inmate of Green Dolphin St. Prison. She then meets Emporio and asks him for change for the bill. Afterwards, she and Emporio meet Narciso Anasui's counterpart Anakiss and Jolyne's counterpart Irene, who invite them to ride with them in exchange for Hermes's money for gas. Hermes feels skeptical at first, as her older sister told her not to ride with strangers, but the coming rain forces her to give them the gas money and ride with the group. The group later picks up Weather Report's counterpart after refilling the car with gas.

Trivia

 * She surgically enhanced her breasts to hide money.
 * She is the first female protagonist in the series to have dreadlocks.
 * The marks on her forehead and chin are scars.
 * Her Steel Ball Run alter-ego is unnamed, although she still acts the same.
 * Due to her rather masculine manner and appearance, Hermes has gotten the endearing nickname aniki (big bro) among Japanese fans.
 * Araki considers the fan nickname a compliment for Hermes because, "It means she looks tough enough to take a real punch and still be in the fight".
 * Her Steel Ball Run counterpart says how her sister told her not to take money from strangers, this means that the counterpart of Gloria Costello, Hermes' sister, is alive & well.
 * Both Hermes and Polnareff have a similar reason to fight, both wants to avenge their sisters. They appear together as rivals in one of the Jojo's Bizarre Adventure All-Star trailers, with their battle named as "AVENGER AND AVENGER".