Julie Yamamoto

Julie Yamamoto is Ben's primary love interest, and later becomes his girlfriend. On their first date, she discovers Ben's powers, but much to his surprise, she finds it "cool". She wears a black t-shirt mostly hidden under a pink sweatshirt, and a white skirt. When playing tennis she is shown wearing white wrist bands, shirt, and skirt. In Fame, she kissed Ben on the cheek for some encouragement. In Hero Time, he saved her life and called her "his girl" and she smiles.

Ben 10: Alien Force
She first appears in Ben 10 Returns: Part 1, where she congratulates Ben after his team won a soccer game.

In Pier Pressure, Ben asked her out on a date to the pier. It was interrupted by an alien (whom they named Ship at the end of the episode), 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" named, Baz-el, who's 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 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 motor scooter and alerts Gwen and Kevin (who were on their way to Gwen's school dance) on Gwen's cellphone and 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 species), and Kevin teases Ben about being a "mother". As Julie takes Ben home on her motor scooter, 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 and 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 in Ship after giving Ben a loving smile.

In Vreedle, Vreedle, 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 aggressive, and Ben and Kevin go in martial court 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 has the ability to "merge" with Julie, giving her an powerful robotic battle suit she can use to fight them. Ben is eventually able to get the judge's favor, and Baz-el reluctantly accepts Ship is now Julie's.

In Single-Handed, Julie "finds" Ben's hand and takes it to Gwen and Kevin. She later uses the serve as Diamondhead to fight Sunder. During the fight Gwen helped her keep Ben's hand away from Sunder but 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.

In the The Final Battle: Part 1 she is briefly seen playing with Ship when Gwen calls Ben because Kevin hadn't shown up.

Ben 10: Ultimate Alien
In Ben 10: Ultimate Alien, Julie is now sixteen-years old, and will again be helping Ben's team from time to time. In the first episode of the series, Fame, she comforted Ben when his identity was revealed to the world. When he thought everybody hated him, she kissed him on the cheek (their first on-screen kiss) and told him that not everybody hated him. Also, Gwen is now Julie's best friend. In later episodes, Julie became more skeptical of Ben when the fame slowly goes to his head, which causes friction in their relationship. In the second episode, Duped, Julie became very upset with Ben for not spending time with her, as he chooses to watch the movie version of "Sumo Slammers" as his real self while leaving an immature version of him with her. In Hero Time, she was no longer angry at Ben, but she became jealous of Jennifer Nocturne after she kissed him whe he saved her life. Later, she was kidnapped by Captain Nemesis. When he tried to kill her and Jennifer, Ben (as Goop) saved Julie (Jennifer Nocturne was saved by Gwen and Kevin). Ben then called her "his girl", as she smiles, confirming that they are back together and Julie forgave Ben for his flaws. She then assisted in taking down Captain Nemesis (now going by the name of "Overlord").

In Absolute Power: Part 2, she use Ship's to help Gwen escape Kevin. She later appeared in battle armor. As shown in a preview on the official website, Julie and Ben were going through relationship troubles. More light on this was shed in Eye of the Beholder. By the end of the episode, Ben apologized to Julie for being such a jerk and he promised to try to be a better boyfriend, which makes both of them happy again, therefore resolving their relationship troubles.

In Revenge of the Swarm, when Ben and Julie arranged a date, she was kidnapped by the Nanochips at the behest of Elena Validus, who was jealous of her. When Ben managed to free Julie before Elena used the swarm in an attempt to suffocate him, 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 watches Elena kill herself to stop the Nanochips and Ben's life is saved. As he mourns Elena's supposed death, Julie comforts him before they both drive home.

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

In Vreedle, Vreedle, her pet Galvanic Mechamorph, Ship, reveals that it can "merge" with Julie. When Ship enveloped her, he became a battle suit. In this suit, she demonstrates superhuman strength and great damage resistance, as well as the power and ability to fire various powerful weapons. It also seems that Ship would be the one controlling the armor as Julie commands it.

In The Eye of the Beholder, it turns out that Julie seems to understand what ship says to her all though he only says, "Ship, Ship, Ship."

Ben 10: Alien Force

 * Ben 10 Returns: Part 1 (first appearance)
 * Pier Pressure
 * Good Copy Bad Copy
 * Save the Last Dance
 * Pet Project
 * War of the Worlds: Part 1
 * War of the Worlds: Part 2
 * Don't Fear The Repo
 * Single-Handed
 * The Final Battle: Part 1

Ben 10: Ultimate Alien

 * Fame (first re-appearance)
 * Duped
 * Hero Time
 * Absolute Power: Part 2
 * Eye of the Beholder
 * Revenge of the Swarm

Trivia

 * Julie is from Japanese descent, as her last name is "Yamamoto ," which is a common surname in Japan.
 * Julie owns a motorized scooter.
 * Julie resembles a character that was on a series called Friends, also called Julie, a beautiful Asian-american girl, with almost the same personality.
 * Her galvanic suit has a strong resemblance to the Samus Aran's Chozo Powersuit even to the point of having similar weapons. Exactly how this transformation is possible is as yet unknown, as it was previously stated that Mechamorphs cannot combine with living organisms. However, when Ship turned into a suit, he was not fused with her.
 * Ben and Julie shared their first on-screen kiss (though only on the cheek) in the first episode of Ultimate Alien, Fame. Also, according to Dwayne McDuffie, they might be sharing a lot more kisses in the further episodes of season 2.
 * Like Ben, Julie has not been shown to have a change of clothes in the Ultimate Alien series.
 * Gwen considers that Julie is the "only one who has common sense among the four of them" (note how by "four", Gwen includes herself), as she always avoids getting in trouble.
 * Julie in many episodes, acts as Ben's "voice of reason". It's also shown that no one can comfort Ben better than Julie.
 * Like Ben, Julie also likes chili fries, smoothies and Sumo Slammers.
 * Ben and Julie's relationship is very popular among fans, and it is often referred as "Benlie".
 * Yamamoto Japanese: meaning ‘(one who lives) in the mountains’ or ‘at the foot of the mountain’, this is one of the ten most common surnames; it is found predominantly in central and west-central Japan.
 * It is confirmed in this link that Julie's family is from Denver.
 * Unlike other characters, Julie has no highlights in her eyes.
 * Julie can somehow understand Ship's onomatopoeic language.
 * When Julie appeared in Revenge of the Swarm, she seemed to have no jealous feelings of Elena trying to to keep her away from Ben until she convinced Elena to save his life, but in Hero Time, you can see her being jealous towards Jennifer Nocturne, that she still cares for Ben. It's possbile she had learned of Elena just recently in Revenge of the Swarm when she was kidnapped, until Ben saved her life.
 * Every episode that Julie shows up until now, Ben "always" uses Humungousaur or Jetray or both.