Well, it depends on how it's written. If it focuses on positive aspects like friendship, adventures, and character development within the Ben 10 universe, it can be appropriate. However, if it involves inappropriate or adult - themed content, then it's not acceptable, especially in a public or general - audience context.
Ben Tennyson is the central character. He has the ability to turn into various ultimate aliens, which is a big part of the story. Gwen Tennyson, his cousin, might also be a main character as she has her own powers and often helps Ben. And then there could be Kevin Levin, who has powers related to absorbing matter. These three characters often work together to face the threats in the 'Ben 10: Ultimate Alien' universe.
One idea could be exploring the backstories of the aliens more in - depth. For example, how did Four Arms become so strong? Another could be a story where Ben has to team up with his enemies to fight a greater threat. Maybe Vilgax and Ben have to work together against an even more powerful alien race.
Well, aside from the main trio, characters like Vilgax are often included. He's a powerful villain and can create a lot of conflict in the story. Grandpa Max is also a good character to add. His wisdom and experience can guide Ben in difficult situations. And then there are the aliens themselves. For example, Rath is a very popular alien form of Ben, and fans like to write stories that focus on his wild and unpredictable nature.
In the 'Ben 10' series, Ben Tennyson is the main character. He has a device called the Omnitrix which allows him to transform into various alien forms. Gwen Tennyson is Ben's cousin. She also has magical abilities and often teams up with Ben in their adventures.
Heatblast is really cool. He can generate and control intense heat, which makes him great for combat and for melting things. He has a flaming body which gives him a very intimidating look.
Fourarms is really cool. He's big and strong with four arms, which gives him great power in combat. Heatblast is also amazing as he can generate and control fire.
Gwen would be a great character to pair with Alien X. Her magical abilities could complement Alien X's powers in interesting ways. For instance, when facing a threat that requires both brute omnipotent force and the finesse of magic. Another good pairing could be Kevin. His ability to absorb and use different forms of energy could interact with Alien X's power source in unexpected ways, like when they need to combine their powers to break through a powerful energy barrier.
One plot idea could be that Ben discovers a group of alien females (and males if you want to be inclusive) who are all lost on Earth. He helps them find their way back home while they all teach him about their unique alien abilities and cultures. They form a kind of friendship group, or 'harem' in a non - romantic sense, and together they face off against villains who are after their powers.