Anne

The unnamed runaway girl, or as the anime calls her, Ann, is a minor ally appearing in Part III: Stardust Crusaders.

Appearance/Personality
Ann first appears disguised as a boy, but later has her real identity revealed. She 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 on 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 especially seen in the battle against ZZ, where she screams for help instead of using the time she had to run.

History
Ann 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
Ann 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.

She 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 Ann 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 Ann; 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 them 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.

JoJo's Bizarre Adventure: Heritage for the Future (PS1/DC/Arcade Game)
Much like the story, Ann appears on the events from Dark Blue Moon, Strength and Wheel of Fortune.

On both Dark Blue Moon and Wheel of Fortune she only appears during cutscenes. Ann makes a major appearance during the mini-game from the Strength events, as the player must shoot Forever the Orangutan. Sometimes Ann appears during the mini-game, if she is hit, then the player loses some health. She also appears after the event is cleared, on the chapter ending's cutscene.

It must be noted Heritage for the Future marks the first and only time Ann appears in a game, since her appearance and role were completely removed from the SNES game.

Trivia

 * Despite not being named in the manga, the end credits of episode 6 of the Stardust Crusaders anime lists the runaway girl's name as "Ann."