Julie Yamamoto

Julie Yamamoto is primarily Ben's love interest, and later becomes his girlfriend. She wears a black t-shirt mostly hidden under a pink jacket, and a white skirt.

Alien Force
She first appears in " Ben 10 Returns (Part 1) " and later in "Pier Pressure". She returns in season 2, in "Good Copy, Bad Copy", "Save the Last Dance" Pet Project" "Dont fear The Repo "Single handed and possibly more in season 3". In "Ben 10 Returns (Part 1)", she congratulates Ben after his team won a soccer game.

In her second appearance, Ben asked her out on a date to the pier. It was interrupted by an alien named Ship, who kidnapped Julie. During the rescue attempt, Julie found out about the Omnitrix, which she finds fascinating. In the end, it was revealed that Ship was trying to lead Ben to his 'Creator', who's ship crashed and was about to explode. Ben and Julie helped fix The Creator's Ship and he left Ship (the alien) with them, saying that he and Ben have a bond. On the walk home, Ship takes off after a passing truck, and Ben and Julie walk home, holding hands.

In "Save the Last Dance", when Big Chill takes control of Ben's personality and starts trying to eat every metal object in sight, Julie follows him on motorcycle and alerts Gwen & Kevin (who were on their way to Gwen's school dance) using her cellphone. She tells them where Ben is headed. Gwen and Kevin manage to subdue Big Chill, only to discover that Big Chill was only building a nest for eggs he had laid. The eggs hatch into infant Necrofriggians (Big Chill's race), and Kevin teases Ben about being a "Mother". As Julie takes Ben home on her motorcycle, she unsarcastically tells Ben that she thought he made a great "Mom". Ben also stated she gets straight A's. In "Pet Project" it was revealed that she is keeping Ship as a pet. She also plays tennis as a hobby, as seen in "Pier Pressure".

In "War of the Worlds" Julie helped Ben fight against the Highbreed invasion. It turned out that she apparently had a curfew. She also seems to show a deal of concern and care for Ben. In "Save The Last Dance", she hugged him after he went missing. In the end of "War of the Worlds", Ben and Julie get close to kissing, but decide against it, as Gwen, Kevin, and Max were all looking on. Ben then tells her that he will walk her to school the next day, and Julie gets home by riding Ship. In "Don't fear the Repo", two alien henchmen, the Vreedle Brothers, are hired by Baz-El (Ship's original master) to get Ship and bring him back. As Julie refused, the Vreedle Brothers started being more agressive, and Ben and Kevin go in martial court to claimed their right on Ship against Baz-El, while Gwen stay on Earth to keep Julie and Ship. When the Vreedle Brother come back, Ship reveal he has the abilitie to "merge" with Julie, giving her an powerful robotic battlesuit she can use to fight them. Ben is eventually able to get the judge's favour, and Baz-El reluctantly accept Ship is now Julie's.

In "Single-handed", Julie "finds" Ben's hand and takes it to Gwen and Kevin. She later uses the seve        as Diamondhead to fight Sunder.

Powers and abilites
Being an ordinary human girl, Julie doesn't have special powers for herself, though she's quite good at tennis, and shows some fighting ability in "Pet Project" (comparing her weapon to a tennis racket). However, she's the only one able to fully control Ship, making her a competent ally.

In "Don't Fear the Repo", Ship reveals that he can "merge" with her, giving her a powerful mecha-like battle suit. In this suit, she demonstrates superhuman strength and durability, as well as the ability to fire various powerful weapons.

Trivia

 * She could be Ben's future wife instead of Kai, since the future shown in "Ken 10" & "Ben 10,000" was just an alternate future/timeline.
 * She is of Japanese heritage, as her last name is "Yamamoto" which is a well common surname in Japan.