Goku's power is measured in different forms and levels in his universe. When it comes to Legendary Pokemon, some of them have the ability to control elements like time and space. In a fanfic, Goku in his Super Saiyan Blue form might be able to match the power of a Legendary Pokemon like Palkia, which has power over space. But it also depends on the situation. If Goku is in an environment where his Ki attacks are less effective, like in a dimension where psychic powers are dominant, he might have a harder time against a Legendary Pokemon like Lugia. Overall, it's a complex comparison as their powers are quite different in nature.
One idea could be that Goku arrives in the Pokemon world by some sort of interdimensional rift. He might be confused at first but then start to explore the concept of Pokemon battles. He could use his martial arts skills to train Pokemon in a unique way, like teaching them special combat moves. For example, he could train a Pikachu to use a move similar to his Kamehameha, but in a more Pokemon - friendly version, like an electric blast with a similar charging motion.
Goku's powers are on a completely different level compared to most characters in Highschool DxD. His Saiyan abilities like Super Saiyan transformations give him incredible strength, speed, and energy projection. In contrast, the characters in Highschool DxD mainly rely on magic and their devil or angelic powers which, while powerful, are not on the same scale as Goku's in terms of raw power. For example, Goku could easily defeat most low - level devils with a single punch in his base form.
Goku's powers are on a completely different level. His Super Saiyan forms would make him extremely powerful compared to most Naruto characters. His ability to fly and shoot energy blasts would be like nothing they've ever seen. Even Naruto in his strongest forms might struggle against Goku.
Well, Goku's power level progression could be different in that he might be more in control of it. Since the head injury had some impact on his psyche, without it, he could have a more calculated approach to increasing his power. He might not rely as much on the Kaioken technique, which was developed in part due to his need to overcome limitations caused by his injury - affected development. Instead, he could focus more on pure Saiyan power - up methods like the Great Ape transformation and evolving it further.
Goku's fighting style might become more fluid. Female characters are often depicted as having more grace in movement, so Goku as a girl could incorporate some elegant dodges and strikes into her already powerful combat techniques.
Goku's powers are on a much higher scale. His ability to destroy planets as a Super Saiyan makes him far more powerful than Naruto at his strongest. Naruto's jutsu are mainly focused on the ninja world, while Goku's powers are universal.
It might be due to a miscommunication. Humans and Pokemon don't always understand each other perfectly. If the Legendary Pokemon misinterprets human actions as hostile, it could lash out. For example, if a group of humans are doing some large - scale construction near its home and it thinks they are about to invade, it may attack.
Often, in 'Goku Harem Fanfic', Goku becomes more aware of his romantic side. He might be a bit more in tune with the emotions of the female characters around him compared to his original portrayal in the Dragon Ball series, where he was mostly focused on fighting and training.
Well, Goku's super strength and fighting abilities could make him a powerful ally or a formidable foe in the Naruto world. His ki powers might be seen as a strange new form of chakra. He could also teach the Naruto characters some of his unique fighting techniques, like the Kamehameha wave.
Their relationship could develop into a deep friendship. Goku, being the kind - hearted fighter he is, would likely accept Android 18 for who she is. And Android 18, seeing Goku's strength and good nature, would start to respect him more and more.