Known Love InterestsEdit
Kai first appeared in Benwolf, when Ben caught a glimpse of her dancing a spiritual dance, and was smitten. She was then introduced as Max's friend, Wes Green's granddaughter, they being Navajo descendants. After that Ben made attempts to impress her. However, at the end of the episode, when Ben tries to establish a relationship with her, she tells him that she only admired him as Benwolf, where she could "train" and "tame" him, much to Gwen's annoyance and breaking Ben's heart. The pop-up version of Ken 10 revealed that, in the future, Kai and Ben will get married and have two children.
Main article: Ben Tennyson and Julie Yamamoto
Julie Yamamoto is a Japanese-American girl, who is Ben's primary love interest. She first appears in the pilot episode of Ben 10 Alien Force as a crowd attendant to Ben's soccer match. She is also a tennis player. At the end of the two-part season two finale War of the Worlds, Ben and Julie get close to kissing, but decide against it as Gwen, Kevin, and Max were all looking on. In the series premiere of Ben 10: Ultimate Alien, Ben and Julie share their first kiss; although technically, Julie kissed him on the cheek, which shocks him. Unlike Ben's other love interests in the series, Julie and Ben both shares the same feelings towards each other. Julie genuinely cares for Ben, it is shown she tutors him patiently, copes up with his quirks also his identity and forgives Ben for all the mistakes he made. Ben trusts Julie immensely, behaves shyly in their first date showing how much he likes her and would do anything for her even travel half way across the galaxy to claim Ship even at that time he was worried of her attention span. In the Ben 10: Ultimate Alien Season 2 premiere, The Transmogrification of Eunice, it was mentioned by Ben that they've been having relationship troubles off-screen because of Ben's tendency for self-absorption. In the following episode, Eye of the Beholder, Ben apologizes to Julie for being such a jerk and promises to try to be a better boyfriend, which makes her much happy again. In the season 2 finale, Julie tries to talk Ben down from being corrupted by the power of Ascalon. When Ben finally discards the sword, she kisses him on the lips for the first time.
Elena Validus is one of the Plumbers' kids and a former member of Ben's soccer team. She is mentioned by Gwen as Ben's first crush (though this contradicts what was seen in the original series as Ben met Elena when he was thirteen while he met Kai when he was ten, but this practically didn't count since Kai never actually liked Ben). Ben had to convince his soccer team mates to let her join. She appeared in the live-action film, Ben 10: Alien Swarm.
She also appeared in Revenge of the Swarm where she was served as the Queen of the Hive. Victor Validus attacking Ben at night, and so the trio went to her to her to find whether she knew anything and the nanochips but in vain. Later,when Ben mentioned Julie which made her angry and jealous, and kidnapped her in order to keep Ben all to herself and they almost kissed but her plan was slightly revealed to Ben and he saved Julie. She, being possessed by the Hive Queen, encountered Ben and choked him with the nanochips. However, she was convinced by Julie to not to do so if she had really liked Ben and the true Elena, that still cared for Ben, willingly sacrificed herself in order save Ben, proving how much she liked him and there was still the Elena, that cared for him, to save his life. Ben became sorry for her, understanding how much she had liked him. At the end of the episode, the nanochips reform, so she is still alive.
She appeared in The Perfect Girlfriend, alive, but disguised as Julie. As Julie, she tried to do everything to make Ben happy. Once Ben finds out Julie is Elena he tried to reason with her, he fought her as Ultimate Echo Echo but lost after she choked him with her nanochips yet again. Julie tells Elena that if she kills Ben, then no one can have him. At the end of the episode, Elena retreats into the sewer, "knowing what hate feels like" and promises to return.
Jennifer Nocturne is a 19-year-old famous film actress who appeared in Hero Time, when she had an instant crush on Ben when he saved her then she kisses him from the lips in front of everyone. Later she tried to make up a relationship with Ben for publicity sake and make a better career for herself. Later on, she was captured along with Julie by Captain Nemesis who later had become Overlord. When Overlord had the two of them hanging from a statue, he gave Ben the option to only save one of them before blasting the cord holding them. Without any hesitation, Goop saved Julie while Kevin and Gwen saved Jennifer. Jennifer had a crush on Kevin at the end of Hero Time, but when he caught her, Gwen got jealous of her and said "I will peel you like a grape!"
In Catch a Falling Star, Jennifer has lost all feeling for Ben, instead having an obsessive attraction to Overlord. When Ben tries to apprehend the villain, Jennifer tries to kill him.
Eunice is a prototype for the Omnitrix called the Unitrix. She can absorb animal and aliens abilities (like bear strength, rabbit agility, and snake flexibility). Ben and Kevin started flirting with her. Eunice stated that Ben was bad at flirting. But in the end Ben let her go because she is a Prototype Omnitrix and quite possibly dangerous and also due to holding Gwen's DNA which is related to his own blood that was sampled and randomized (Azmuth at Ben's insistence decided to compromise and bring her to be Azmuth's assistant). Before Eunice leaves with Azmuth, she gives Ben a blue flower as a reminder of her. In Simian Says, Eunice kissed Ben on the cheek.Emily briefly dated Ben. The reason they broke up was that Ben went "hero" and left Emily on a 200 ft watchtower. Now Emily hates Ben. It is said by Ben and Emily that Ben had webbed her to the top of the tower with Spidermonkey. This implicates that Ben and Emily dated sometime between the first episode of Ben 10: Ultimate Alien and this episode because Emily knew Spidermonkey during that time.
In Many Happy Returns, when Kevin was about to marry her when Ben challenges Looma to a battle. She still defeated him until he turns into Four Arms. But, Ben defeats her, and it is revealed that female Tetramands marry the ones that beat them in battle. Kevin and Gwen leave, and Looma says she'll be back in three years. Ben mutters that Kevin is "so dead".
In Rules Of Engagement, Looma returns attempting to collect four items for their wedding, specificly something conquered, bruised, severed, and blue. Looma battled the tribe of Ester to capture one of them as something conquered and Ester asked Ben for help. Looma was happy to see Ben again, but was busy with collecting the items. Ben tried to stop her, but she tossed him aside and took the Ester, Rook, Julie and Julie's boyfriend, Hervé, for being a photographer. She also captured Fistina's right hand, which leads Fistina and Ben getting it and "Little Rook" back. Looma went to Ben's house and was happy to see her "mother-in-law" and presented her "offering gifts". When the "offering gifts" tried to escape, Looma tried to re-capture them. Looma fought Julie when she heard that she is Ben`s girlfriend, not knowing that they broke up. With the help of her friends, Julie was able to defeat Looma. Looma was saddened, but accepted her defeat. However, Looma promised Julie to crush her skull next time her and Julie meet again.
When Ester first met Ben in Hot Stretch, they fought for the fusion device. Later when she realized her kind was doing evil things, she joins Ben's team. She brought him to her friend's town and they played an alien version of hockey. Ben turned into Water Hazard and splashed everyone with water to cool them down, even when Ester told him not to. He then brought her a towel, and she blushed as he gazed at her. She turned the water floating around him into snowflakes, and ran laughing. Rook told Ben she liked him. Later when her kind realized she was the chief, she hugged Ben and told him she and her kind would be good neighbors. Later Ester's friends called Ben her boyfriend, and Ben first denied it but then excitedly asked Rook if he had a chance with her.
In Rules of Engagement, Ben offered to help clean up the Hot Spot with her. She excitedly agreed, wrapping her arms around his arm. She also stated that she herself is fond of Mr. Smoothy. According to Derrick J Wyatt, they go on a date in episode 51.
In Showdown: Part 1, Ben says that his first crush is Patty Berkenfeld from 3rd grade. Not more is known about her.The Frogs Of War: Part 2, Ben as Bullfrag infiltrates her team, and from the moment she saw him, Attea had grown a little crush. When they meet in the cell block of Plumbers HQ, Ben comes up to her and starts flirting, taking note that his new form shows her in a whole new light. Attea is at first a bit flustered, but starts flirting back, only to be knocked out by a mana blast by Gwen. Ben says that only happened because he was being influenced by the Incursion DNA.
At the end of the episode when leaving earth, she gives Ben the offer to come with her and "Ditch that monkey face and turn into Bullfrag again" He promptly declines. Attea gives him a frog-like kiss to the back of his head with her long tongue, winks, and takes off.