It's likely Saitama. His power is to defeat any enemy with one punch, which is an extremely overpowered ability. Even though Ben has a wide variety of powerful aliens in his Omnitrix, none of them seem to have an ability that can match Saitama's sheer strength and simplicity of his power.
However, it could also be argued that Alien X from Ben 10 might be a contender. Alien X has near - omnipotent powers, being able to manipulate reality on a vast scale. But Saitama's power is more straightforward and combat - focused. In a direct fight, it's hard to say whether Alien X could even react in time to Saitama's punch before being defeated.
It's hard to say, but Goku would be a top contender. His ability to constantly power up and reach new levels of strength like Super Saiyan God and Ultra Instinct is insane. But Ben in his Alien X form from the Omnitrix also has near - omnipotent powers. So it could really go either way depending on how the fanfiction writer sets up the battle conditions.
Well, it depends on the context. If the battle takes place in the Naruto universe, Naruto might have an advantage as he is more familiar with the terrain and can use chakra - based attacks that Saitama may not fully understand at first. For example, Naruto could use shadow clones to surround Saitama and then attack with a Rasengan. But Saitama's raw power is still a huge factor. In the end, it could go either way depending on how the author writes the story.
It's hard to say for sure, but Ruby could be a very powerful character. Her speed and scythe skills are already formidable in the RWBY universe, and if she were to gain some of the combat knowledge from For Honor, like the strategic thinking of a For Honor general, she could be extremely powerful. She might be able to quickly analyze her opponents' fighting styles and counter them effectively.
In this crossover fanfiction, determining the strongest would be complex. Saitama's power is a mystery even in his own universe. He doesn't seem to have a limit. Goku, on the other hand, is always pushing his limits and reaching new levels of power. Vegeta could also be a factor. His pride and determination might lead him to try and take on Saitama. But Saitama's lack of interest in prolonged battles might make it difficult for any DBZ character to fully gauge his strength. So, it's really hard to say who would be the strongest in this crossover.
It's a tough call. Goku has the ability to keep getting stronger through training and achieving new forms like Ultra Instinct. However, Saitama has shown that he can defeat any opponent with one punch so far. But Goku's powers are more defined in terms of levels and growth potential. So, it's hard to say who would be the strongest in a crossover. It could depend on the situation and how the writer wants to portray their encounter.
I think it could be a combined form of a character. For example, if Issei were to somehow gain the power of the Nine - Tailed Fox. He already has his Boosted Gear and his experience in battles in the Highschool DxD world. Adding the Nine - Tailed Fox's chakra would make him an extremely formidable opponent. He could use the fox's chakra to enhance his Sacred Gear even further, and his new form might have abilities that are a combination of both universes, like using the fox's tails as a weapon while also having the power of the Boosted Gear.
It's really hard to say. Goku in his Super Saiyan Blue form has incredible power and can destroy planets. But Naruto in his Six Paths Sage Mode also has amazing abilities. However, if we consider raw power, Goku might be more powerful as he can reach levels of power that can destroy entire solar systems. But Naruto's intelligence and his ability to strategize could give him an edge in a fight.
It's really hard to say. Naruto has some extremely powerful characters like Naruto himself with his Nine - Tails chakra and Sage Mode. But in Yu Yu Hakusho, characters like Yusuke at his Mazoku form are also incredibly strong. It might depend on how the crossover is written. If the power - up systems are combined in a certain way, it could be a character who manages to blend both types of powers most effectively.
However, one could also argue that Alien X from Ben 10 Omniverse, if combined with Naruto's willpower and determination, would be the most powerful. Alien X has reality - warping abilities, and Naruto's strong spirit could potentially control and direct those powers in ways that we can't even imagine in the context of the fanfiction.
It expands the universe by exploring the backstories of the characters more deeply. For example, we might learn more about the childhood of characters like King. It also creates new scenarios for the heroes to face, like battles in different dimensions. This gives more depth to the world of One Punch Man.