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Familyoriginal series, Ben and Gwen have been known for always bickering or arguing and fighting, and they have a love/hate relationship. However, deep down they really do care about each other as shown in Secret of The Omnitrix when Ben would go far lengths to keep Gwen out of danger such as going Four Arms despite the fact that the Omnitrix's S.D.M count down would only accelerate. And when he found out that she was still alive, he ran through the open field of heavy fire in order to hug her.
In Alien Force, they have stopped their hostile fights and have been revealed to be their favorite cousins respectively. In Time Heals, Ben once more reveals his caring attitude towards Gwen after she frees him from a torture chamber created by Hex or Charmcaster. He states that he "already lost her once and doesn't want to lose her again." He then buys Gwen some time in order to allow Gwen to reverse her faults and restore time back the way it was.
In Ultimate Alien their relationship has once more received an upgrade as shown in Greetings From Techadon. While at Mr. Smoothy, both of them talk about how they were when they were 10 and how they used to not get along and then soon laughed at the things they did as younger kids. In The Ultimate Sacrifice, they have bonded so much that he kisses Gwen goodbye on her forehead (something the 10 year old Ben wouldn't do) before jumping into the fire pit to free his original Ultimate Forms.original series, Ben's relationship with Max seems to be father-son (this is because the majority of the series took place in the summer and Max was the only guardian available). When he was seriously injured, Ben went full strength with Four Arms and brutally destroyed Vilgax's robot drones as they were the catalyst for his injury. His relationship with his grandfather has not changed much at all during Alien Force and Ultimate Alien.
Carl and Sandra Tennyson
Ben has stated that he loves and cares about them and that they're good parents and raised him well enough to become the person he is today.
In the original series, Ben met Kevin when the game he was trying to play "ate" his money. From there, Kevin appeared and used his powers to give Ben some tokens. Despite a warning from Gwen, Ben runs away with Kevin into the streets of New York City. After nearly getting caught by police for trying to steal a Sumo Slammers video game before it came out, The two form a "partnership" and proceeded to rob a train full of money. Ben finds out that the train had people in it and decides to stop Kevin from killing innocent lives causing a fight between Heatblast and a Pyronite mutated Kevin. Ben successfully stops the train's collision, but Kevin escapes and goes loose on the city. After being picked up by Max, the trio go to where Ben expects Kevin to be and soon a fight between Fourarms and a Tetramand mutated Kevin begins. After loosing, Kevin fakes wanting to join Ben and the others in order to try to steal the Omnitrix only to seemingly fail. It's then revealed that Kevin had actually absorbed the alien's abilities. Throughout the rest of the series, Kevin was constantly tormenting the trio and trying to kill Ben every week as stated by Ben in Perplexahedron.
In Alien Force, Ben doesn't trust Kevin at first, but he then learns to trust him enough to allow him to join his team which happened because of the events of a future episode. During this series, they shared a friendly rivalry.
In Ben 10 Returns, Ben and Gwen find Kevin making an illegal deal with other aliens. After a fight in which the Omnitrix changes, Ben and Gwen ask for Kevin's help in taking down the group of aliens. At the end of the episode, Kevin agrees to join Ben's team. There relationship continued to grow as the first season went on when Ben helped Kevin get ready to go to Gwen's school dance.
In Ultimate Alien, their bond has become more stable than before. But in Absolute Power: Part 1, Ben sees that he needs to kill Kevin in order to prevent him from hurting more people. This caused Ben to become a ruthless person despite the fact that his facial expression changes to a positive one when Darkstar reveals that there's a way to cure Kevin. In the end, the two go out for smoothies after their short quarrel. In Ultimate Sacrifice, Kevin admitted that Ben is truly his best friend.
At first, Ben didn't like the fact of having a new partner, and felt like Rook was just trying to replace Gwen and Kevin. However, he soon began to like Rook. In A Jolt From The Past, Ben seems to care a little about him as he shouted his name when Fistrick knocked him out. In Of Predators And Prey: Part 1, they have their first fight when arguing over which plan to carry out to find Zed. Ben even went as far to say he never wanted Rook, but this was revealed to be a ruse to make Khyber show himself. They eventually work well together with their respective strengths covering each other's weaknesses, and they share a good camaraderie and love for smoothies. In Many Happy Returns, Ben states, "I don't always get him, but he's cool", to which Rook replied that the feeling was mutual.
Ben's initial thoughts of Azmuth before meeting him was never stated, but he did find it to be somewhat ironic that he was a Galvan despite the fact that he's seen what Galvans can do while he's Grey Matter. After meeting him, he thought of him as a jerk who cared about no one but himself. However, his attitude changes when Azmuth fixes the Omnitrix.
In Alien Force, Ben meets Azmuth again only when the situation was important (e.g. War of the Worlds). Ben sees him as another mentor and follows his advice (at least until season 3). During Season 3, Ben loses Azmuth's trust in the second episode.
Ben's relationship with Professor Paradox is actually quite simple and he sees Paradox as a guide when Azmuth or Grandpa Max isn't around. Throughout the series, Ben has received advice from Paradox about upcoming future events (even one that is possible).
Ben met Rex in Ben 10-Generator Rex: Heroes United mistaking him for an alien and Rex mistaking Ben as an EVO. The two continued to be enemies until they both realized who the real enemy was. They eventually share a friendly bond and explain how they came to be who they are. Once Ben leaves, he is hoping to see Rex again one day and vice versa.
Particularly because of Tetrax being Diamondhead's species, they have shown help to each other, such as in the episode Hunted.
Kai first appeared in Benwolf, when Ben saw 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 Blitzwolfer, 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 a possible 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 watching them. 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 have feelings for each other. Julie genuinely cares for Ben, it is shown she tutors him patiently, copes up with his quirks, fame 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 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 Eye of the Beholder, Ben apologizes to Julie for being 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 discards Ascalon, she kisses him on the lips for the first time.
In Rules Of Engagement, it is revealed that Ben and Julie have "broken up" some time ago, but they agree to stay as friends.
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, and Rook says his first crush is someone else). Ben had to convince his soccer team mates to let her join. She appeared in the live-action film, Ben 10: Alien Swarm.
Elena also appeared in Revenge of the Swarm where she was served as the Queen of the Hive. Victor Validus was 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 revealed to Ben and he saved Julie. Elena, being possessed by the Hive Queen, encountered Armodrillo 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.
Elena 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 Nanochips again. Julie tells Elena that if she kills him, 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 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 public. 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 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, when he caught her, but Gwen got jealous of her and said "I will peel you like a grape!"
Eunice is a prototype for the Omnitrix called the Unitrix. She can absorb animal and aliens abilities (like bear strength, rabbit jumping skills, 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 Unitrix and quite possibly dangerous and also due to having Gwen's randomized DNA which makes her technically related to him (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 Spidermonkey had webbed her to the top of the tower. 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.
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 is fond of Mr. Smoothy.
Sometime before Return to Forever, they went on a movie date.
According to Derrick J Wyatt, they go on a date in episode 51.
In Many Happy Returns, when Kevin was about to marry her when Ben challenges Looma to a battle to stop it. She keeps defeating him until he turns into Four Arms. But, when Four Arms defeats her, it is revealed that female Tetramands marry the ones that defeat 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, something bruised, something severed and something blue. Looma battled Kraaho 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 Ester, Rook, Julie and 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 future "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.
in Showdown: Part 1, Ben says that his first crush is Patty Berkenfeld from 3rd grade.The Frogs Of War: Part 2, Bullfrag infiltrates her team, and from the moment she saw him, Attea had grown a crush. When they meet in the cell block of Plumbers HQ, Bullfrag comes up to her and starts flirting, taking note that his new form shows her in a whole new light. Attea is a bit flustered, but starts flirting back, only to be knocked out by a mana blast by Gwen. Bullfrag says that happened because he was being influenced by the Incursean 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.
In T.G.I.S., Ben gains a crush on Drew Saturday the minute he saw her and nervously tells her, "Meeting you is the good". Drew responds by saying, "Right back at you". Then, when Doc tells Ben, Rook, Zak, and Fisk that Dr. Animo and his chupacabra army are attacking Mr. Baumann's store, Drew offers to stay behind to look after the petrified alien. Ben though suggests that Rook stay behind and Drew come with him, telling them that they might need her medical expertise. Later, when Ben, Rook, Zak, and Fisk arrive at the airship to stop Argost and his army of cryptids, Doc and Drew reveal themselves and tell them that they escaped moments before Argost showed up. Ben then instantly tells Drew that he's happy that she's ok, causing Zak to tell him that Doc is ok too. At the end of the episode, Ben tells Zak how it was a pleasure to work with him and his mom. He then takes a photo with Zak, Doc, Drew, and Fisk as Fourarms. Ben has a crush on her, but Drew doesn't return his feelings. She knows about his crush and finds it cute and amusing, but Zak doesn't appreciate his crush, but still remains his friend.
Ben has a rivalry with Vilgax, but has shown to be helpful for him when Vilgax is in desperate need of help.
Albedo has a great hatred for the team, especially Ben but he doesn't hate Albedo as much. It is revealed that in Trouble Helix, they were once allies.
Ben used to underestimate Animo until the 4th season. Once Alien Force had him appear, Ben saw him as a good threat seeing the condition of the Null Void. In Ultimate Alien, he states that years ago, he thought his plans were dumb. In It's Not Easy Being Gwen, he underestimated him therefore calling Gwen for help.
Mr. Baumann is Ben's old neighbor, but they are shown to have a mutual dislike for each other. Mr. Baumann hates Ben, constantly accusing him of destroying his car and other property of his. In return, Ben hates Mr. Baumann for blaming him for destruction that was not his fault.