Anne

The otherwise unnamed runaway girl is a minor ally appearing in Part III: Stardust Crusaders.

Appearance/Personality
The unnamed runaway girl first appears disguised as a boy, but later has her real identity revealed. The girl is shown to be a complete liar, telling lies to the Joestar group multiple times, but people barely fall for her stories. She is also a confident swimmer, believing she could reach shore swimming from the middle of the ocean. She eventually develops a crush towards Jotaro Kujo, and constantly tags along with the group.

However, she isn't prepared for the group's dangerous trip, becoming heavily dependent on them to survive. as foretold by Jotaro, she only drags them down to the point of risking their own lives. This is expecifically seen in the battle against ZZ, where she screams for help instead of using the time she had to run.

History
The girl known simply as "The Runaway Girl" is a girl who wanted to travel the world, believing that posing as a boy would make it easier. She believed that once she had grown enough she would need to start wearing a bra, making it difficult to pose as a guy at that point. She then runs away, claiming that the age she is now is the best to travel. Her intentions for doing so has been hinted as due to her crush on Jotaro and "having nothing else better to do".

Stardust Crusaders
The girl first appears as a stowaway on the cruise ship that the Captain Tennille Imposter had abducted. Posing as a boy, she is found by one of the sailors who threatens to turn her to police when they reach shore. She then lies, saying she is going to Hong Kong to meet her father. She realizes that she was going to be imprisoned and  jumps off the ship in a attempt to swim to shore by herself and remain safe. When close to being attacked by a shark (later killed by Dark Blue Moon) she is begrudgingly saved by Jotaro Kujo. It is then that her identity as a girl is revealed and she threatens to cut one of the crew members when the Joestar group thinks she is an Stand user.

The runaway girl is then taken hostage by the Captain Tenille Imposter when his real identity is revealed, but is saved by Noriaki Kakyoin when Jotaro fails to do so and gets dragged into the water. She starts to develop a crush towards Jotaro and his attitude, thinking he is cool.

During the battle the ship is destroyed and she accompanies the group into Forever's stand-bound ship, Strength. Forever, acting like a human being, lusts for the runaway girl and corners her in the middle of her shower soon after brutally killing all sailors. She is saved by Jotaro again and watches their battle.

When the group reaches Singapore the girl refuses to separate from them, saying she will meet her father in 5 days. Under protests at first, they agree to let her accompany them until her father arrives because she was too poor to live on her own. Later on, Rubber Soul poses as Kakyoin and approaches Jotaro and the runaway girl; she eventually notices his strange behavior. Rubber Soul's real identity is revealed and and he is defeated soon after.

On their way to India they left her behind in Singapore to meet her father, but Jean Pierre Polnareff comes to the conclusion that it was a lie and she is probably an orphan. He then claims that it feels lonely without her presence. The girl, however, is revealed to have snuck on the train and is following then again.

The group only encounters her moments before ZZ's attack, asking them for a ride in the middle of the street. It is then that she admits to have run away from her parents in Hong Kong, though the group is more concerned about dropping her off and do not listen. Despite stern warnings from Joseph Joestar about their journey and how she is only going to slow them down, she tags along with the team and tries to bribe them with stolen porn pictures.

In the midst of ZZ's attack the girl ends up tripping while running with the others. Instead of getting up and running, she stays on the floor and screams for help, at which Jotaro complies to do so, but not before scolding the girl for her attitude: she could have easily get up and run again instead of spending her time on the ground helpless without no one holding her down. The group tells the girl they are going to give her money, plane tickets and send her back to Hong Kong as soon as possible. Under protests, the runaway girl has no choice and finally returns to Hong Kong.

Trivia

 * Her SBR counterpart could be the Unnamed girl kidnapped by Sasame Ojirou due to how they are both held captive by a antagonist only to be rescued. Those two also has a similar introduction since they were away from their home as well as being in a perilous situation immediately after their debut.
 * In the grand scheme of things the Runaway Girl didn't have to be kept in the story after the fight with Dark Blue Moon as she does nothing that affects the main plot, does nothing help the team out and, as Jotaro correctly predicted, started to drag them down due to her dependence on them.
 * This is similar for Gwess; a character from Part VI: Stone Ocean (a part which Jotaro was also in but as an ally instead) as after she's defeated by Jolyne Cujoh Gwess doesn't do anything to help the team in Part VI, unlike some past antagonists who join the team as an ally.