Julie Yamamoto's History
Alien Force
Julie first appeared in Ben 10 Returns: Part 1, where she congratulated Ben after his team won a soccer game. She introduced herself and agreed to meet him at school the next day.
In Pier Pressure, Ben asked Julie out on a date. It was interrupted by Ship, who kidnapped Julie. During a rescue attempt, Julie found out about the Omnitrix. In the end, it was revealed that Ship was trying to lead Ben to Baz-l, whose ship crashed and was about to explode. Ben and Julie helped fix Baz-El's ship and he left Ship with them, saying that he and Ben have a bond. On the walk home, Ship took off after a passing truck, and Ben and Julie walked home, holding hands.
In Save the Last Dance, when Big Chill took control of Ben's personality and started eating every metal object in sight, Julie followed him on her motor scooter and alerted Gwen and Kevin. She also told them where Ben was headed. Gwen and Kevin managed to subdue Big Chill, only to discover that Big Chill was building a nest for eggs he had laid. The eggs hatched into baby Necrofriggians, and Kevin teased Ben about being a "mommy". As Julie took Ben home on her motor scooter, she told Ben that she thought he made a great "mom". Ben also stated that she gets straight A's.
In Pet Project it was revealed that Julie is keeping Ship as a pet; it put a strain on her relationship with Ben, as he feared Ship could do something that she couldn't handle. The Forever Knights kidnapped Ship, planning to use him to mass-produce spaceships to go to the Dragon's planet, brainwashing him. Julie managed to get through to Ship and bring him back to his senses. At the same time, she told Ben he wasn't the only one who saw Brainstealers From Outer Space; he skipped a date to watch a marathon of it. Julie would allow Ben and the others to use Ship's new spaceship form if they asked her.
In War of the Worlds: Part 1, Julie helped Ben fight against the Highbreed invasion and it turned out that she apparently had a curfew. She also seems to show a deal of concern and care for Ben. At the end of War of the Worlds: Part 2, Ben and Julie got close to kissing, but decided against it, as Gwen, Kevin, and Max were all watching. Ben then told her that he would walk her to school the next day, and Julie got home by riding Ship after giving Ben a loving smile.
In Don't Fear the Repo, the Vreedle Brothers, hired by Baz-El to return Ship to him. As Julie refused, the Vreedle Brothers started being more aggressive. Ben and Kevin went to Coda Coda to claim their right on Ship against Baz-El, while Gwen stayed on Earth to keep Julie and Ship safe. When the Vreedle Brothers came back, Ship revealed he can "merge" with Julie, giving her a powerful battle suit she can use to fight back against the Vreedle Brothers. Ben was eventually able to get the judge's favor, and Baz-El reluctantly accepted that Ship is now Julie's.
In Singlehanded, Julie found Ben's detached hand and took it to Gwen and Kevin. She later used Diamondhead's hand to fight Sunder. During the fight, Gwen helped her keep Ben's hand away from Sunder but Julie wound up being used in a trade when Sunder caught her. After Sunder was knocked out, she, under Kevin's instructions, held a beam on Ben's arm while they used Sunder's axe to put Ben back in one piece and unknowingly sent Sunder to the Null Void as a result.
In the The Final Battle: Part 1, Julie was briefly seen playing with Ship.
Ultimate Alien
In Fame, Julie comforted Ben when his identity was revealed to the world. When he thought everybody would hate him, she kissed him on the cheek and told him that not everybody hated him.
In Duped, Julie became very upset with Ben not spending time with her, as he chose to watch the movie version of "Sumo Slammers" as his real self while leaving an immature version of himself with her.
In Hero Time, Julie became jealous of Jennifer Nocturne after she kissed Ben when he saved her life. Later, she was kidnapped by Overlord. When he tried to kill her and Jennifer, Goop saved Julie. Goop then called her "his girl", and she smiled. She then assisted in taking down Overlord.
In Absolute Power: Part 2, Julie and Ship helped Gwen escape Kevin. She later appeared in her battle suit for unknown reasons.
Sometime before The Transmogrification of Eunice, Ben and Julie broke up, or "might as well be broken up".
As shown in Eye of the Beholder, Julie and Ben were going through relationship troubles. Ben apologized to Julie for being such a jerk and he promised to try to be a better boyfriend, which made them both happy.
In Revenge of the Swarm, when Ben and Julie arranged a date, she was kidnapped by the Nanochips at the behest of Elena, who was jealous of her. When Armodrillo freed Julie, Elena used the swarm in an attempt to suffocate Armodrillo. Julie was able to convince Elena to stop her Nanochip activity if she really loves Ben, as well as Julie herself loves him. Then, she watched Elena kill herself to stop the Nanochips and Ben's life is saved. As Ben mourned Elena's supposed death, Julie gave him some comfort before they both drove home in Ben's car.
In Greetings from Techadon, Julie and Ben competed in a golf course and Ben won, thanks to Brainstorm, but Julie was shown not to be happy and accused Ben of cheating in the death hole. At the end of the episode, Ben went off to have a rematch as promised to Julie.
In The Flame Keepers' Circle, Julie joined a philanthropic organization called the Flame Keepers' Circle, as she accepted their theology of using Dagon's technology to advance Earth's humanitarian efforts and create a utopia. She tried to get Ben and Kevin to understand but failed, becoming quite angry at Ben for this as he laughed in the Cult Leader's face and he himself uses alien technology to protect Earth. She believed this to the point of pretending to be a hostage for Conduit Edwards to make Ben revert from Big Chill. She again tried to preach the benefits of the Flame Keepers' Circle to Ben, but realized her mistake when Ben told her that "Dagon" was Vilgax. She maintains a belief that alien technology should not be kept from humans although is far less fanatical.
In The Perfect Girlfriend, Julie went off to Europe for a tennis tournament. During that time, Elena impersonated Julie to try and win Ben's heart. Right after Elena revealed herself, Julie arrived at Ben's home, and was able to talk Elena down again when she tried to kill Ben, prompting her to leave, swearing revenge.
In Night of the Living Nightmare, in Albedo's nightmare, Julie and Ship fought Ben and were defeated.
In The Ultimate Enemy: Part 1, Julie was playing a game of tennis when humanity was turned into Esoterica. She was able escape the mass transformation when Ship merged with her.
In The Ultimate Enemy: Part 2, Julie showed up after Ben stripped Vilgax of Dagon's powers and managed to talk him out of selfishly wiping out all evil. After Ben turned all of humanity back to normal, Julie kissed Ben on the lips for the first time in front of the others.
Omniverse
At some point after Ben obtained his new Omnitrix, Julie called him while he playing a video game of Sumo Slammers. Believing that Ben's rude comments towards a game character were directed towards her, she hung up the phone. This indirectly caused the two to break up.
In Rules of Engagement, Julie reunited with Ben and introduced him to her new boyfriend. They are kidnapped along with Ester and Rook by Princess Looma. Julie fought Looma and with the help of Ball Weevil and Ship, she won. Ben and Julie then made an agreement to be friends after the break-up.
In The Most Dangerous Game Show, Julie appeared as one of the females chosen to compete for Ben's hand in marriage. She is utterly uninterested in the contest, texting Hervé for the duration. This causes her to get knocked into the water during the "hole in the wall" round. After being sent to the Null Void with the other losers, she is later freed and returned to Earth.
