Ben Tennyson

Benjamin Kirby Tennyson is the protagonist from the Ben 10 series of TV shows. As he is portrayed in SSPD, he appears as his Omniverse iteration. He was an ordinary boy until finding the Omnitrix, a device that allows him to turn into various alien species. In SSPD, he has also joined the ranks of the Phantom Thieves of Hearts, and has worked with Joker, Mona, and Oracle to change the hearts of Benedict Malton and, currently ongoing, Aika Akagawa.

Appearance
Under normal circumstances, Ben appears wearing a standard black-and-green t-shirt with a 10 on the front. He also wears brown cargo pants, green sneakers, and of course, the white-and-green Omnitrix on his left wrist. He occasionally appears wearing a white hoodie, and on other occasions, a Letterman's jacket gifted to him by Joker.

While perceived as a threat in the Metaverse, his appearance changes dramatically. He wears a green visor of sorts, one which can be removed to summon his Persona, Cryptid. He wears a green shirt with a 10 on it, a black cape with a green fixture around the neck that mimics Cryptid's, a belt with the Plumbers logo on it, black pants, green leggings of sorts, and white boots. The Omnitrix remains on his left wrist, where he also wears a white, robotic-looking glove.

Powers and Abilities
Ben wields the Omnitrix, his greatest source of power. With it, he can transform into over 60 different alien species, most of which enhance at least one attribute of his beyond what his human form was capable of. These transformations can be quite simple, like Heatblast's basic fire abilities and Humungousaur's immense strength, or radical changes, like Big Chill's intangibility, flight, and ice abilities, or Alien X's omnipotence. Some of these aliens alter his personality (Brainstorm, Jury Rigg, etc.), but for the most part, Ben remains in control.

Without the Omnitrix, however, he is no slouch. He has been trained in hand-to-hand combat by his cousin Gwen Tennyson, who uses her own combat alongside him on occasion. He has received a basic Plumbers training (which forbid him from using his aliens), and has been shown to be surprisingly strong and nimble even when human.

The Omnitrix has many failsafes in place to protect Ben. He is, to put it bluntly, incapable of being killed while the Omnitrix is on his wrist (and failsafes also exist to prevent it from leaving his wrist). The AI implanted in it can react in nanoseconds to forcibly transform Ben into an alien that can survive the attack that would otherwise kill him.

While in the Metaverse, Ben wields the power of Cryptid, a physical manifestation of his inner self known as a Persona. Cryptid specializes in Psi Skills, as well as Physical and Gun Attacks. He also uses two-handed swords and laser rifles to fight Shadows. He can still use the Omnitrix, and can use Cryptid alongside it.

In SSPD
Ben was one of the few characters brought over from The Nexus, as Destiny caught wind of his hatred of being there. By the time he had arrived in the chat, he was already well acquainted with Morgana, and was also vaguely familiar with Proto Man, who arrived alongside him. His knowledge of Chara, however, was much lesser.

He became friends with Aika Akagawa, mostly up to the point where it was revealed that she was a hitwoman. While they initially had a falling out because of it, Morgana discovered that her past was rooted in Benedict Malton; a man with a Palace, and thus a man who's heart could be changed. After recruiting Ren "Joker" Amamiya (and later Futaba Sakura, under the alias of Oracle), the team went into his Palace and changed his heart. It was here that Ben awakened to his Persona.

After the fact, Futaba organized a Christmas Party, where Ben grew somewhat closer to N, bonding over their shared reliance on a device for power and their lack of understanding for how it works. Here, Malton's public apology was aired, resulting in Aika's breakdown and, subsequently, N's disappearance. While Ben hated her for throwing away their work, it was clear that she needed help. After confirming that she had a Palace, they teamed up once more and worked to change Aika's heart.

Morgana
Their alliance is the longest standing not just among the Phantom Thieves, but among the entire chat. They first bonded over the lack of heroics in The Nexus, and now find other things to bond over, like stuffing their faces, and the questionable decisions Joker makes at times. The two make a solid team, with Ben serving as incredible brawn and Morgana serving as both incredible brain and the healer for his brash actions. They clash in their ideals rather frequently, but he frequently still voices his thanks to Morgana and enjoys spending time with him.

Joker
The second Phantom Thief Ben met, the two have a steady sort of mutual respect for one another. Ren's stoic nature is something new to Ben, and he's trying to get used to it accordingly, but even so, he finds it rather easy to unwind around him. While usually the leader himself, Ben has little arguments with leaving the running of the Thieves to Ren, and respects his ability to do so, even if he frequently questions some of his decisions.

Oracle
Ben has stated that he sees Futaba similarly to his cousin Gwen, specifically back when they were 10 and he first found the Omnitrix. In fact, her combination of teasing and generally goblin-like tendencies remind him of both Gwen and himself at age 10. For this reason, despite a full-on falling out after Malton's Palace, he's found it easiest to open up to her. Ben considers her his best friend of the Thieves.

N
The two lacked the appropriate amount of time to truly become good friends, but they often bonded over their strange powers in the chat. This came to a head at the Christmas Party, where they had a friendly one-on-one conversation, and Ben felt a close friendship with her thanks to their startling similarities. Before she left, Ben wanted to serve as a sort of tutor to her, given his understanding of the Omnitrix. That hasn't come to be yet, but he still sees her leaving the chat as the greatest casualty of the party.

Aika Akagawa
For a good while, Ben actually considered Aika to be a distant friend of his, even after discovering she was a hitwoman. He failed to see the rage she was repressing while they dealt with Malton's distortions, and believed that she was simply very willing to see their alternative. Thus, even after her questionable past came to light, he continued to be fine with chatting with her and generally bonding with her.

After the Christmas Party, however, Ben has little faith in her. He has grown an incredible disdain for her, due to her throwing away their months of work in changing Malton's heart and her break-down being the primary reason that N left the chat. He frequently voices that he would much rather simply throw Aika in the Null Void, but continues to work with the Thieves to change her heart as well.

Alice
While initially very friendly towards Alice, in part thanks to her keeping an eye on Aika while he was busy with Malton's Palace, Ben's opinion of her has deteriorated quite rapidly. After her attacking him at the Christmas Party, and her raiding the Phantom Thieves shortly thereafter, he rather bluntly hates her, possibly more than Aika. Her actions serve as the only wedge currently between him and the Phantom Thieves, as they want to let bygones be bygones, while Ben wants her to leave the chat for good.

Trivia

 * Ben's Phantom Thief outfit, as well as his Persona, are based off of the Flatwoods Monster, a popular alien sighting.
 * When interacting with Joker, Ben likely represents the Change Arcana.