Evangeline and Goku. Evangeline is a powerful vampire in UQ Holder. Her dark magic and immortality contrasted with Goku's pure - hearted and extremely powerful fighting style would create some interesting dynamics. They could either be at odds, with Evangeline seeing Goku as a threat to her power, or they could end up teaming up in some strange circumstances where their combined powers are needed.
Kuroumaru and Goku. Kuroumaru is a unique character in UQ Holder with a complex backstory. Paired with Goku, Kuroumaru could learn about Goku's unwavering will and determination that comes with his Ultra Instinct. Goku, on the other hand, could befriend Kuroumaru and help them in their own personal journey within the UQ Holder universe, perhaps even helping Kuroumaru become stronger in their own way.
Another storyline could involve a character from UQ Holder learning the secrets of Ultra Instinct from Goku. This would be a great way to blend the two universes' concepts. The UQ Holder character could struggle at first to understand and master it, leading to some comical and also tense moments as they train with Goku. Maybe they have to overcome some personal limitations in order to even begin to access the power of Ultra Instinct.
A possible plot is a crossover with the Naruto universe. Goku in Ultra Instinct mode could be mistaken for some sort of super - powered ninja. He might end up training with the Hokage or getting involved in the Akatsuki's plans. Since his Ultra Instinct gives him such incredible reflexes and power, he could easily hold his own against the strongest ninjas like Naruto in his Six Paths Sage Mode or Sasuke with his Rinnegan. It would be a clash of two very different power systems.
Well, with Ultra Instinct, Goku would be able to react extremely quickly to the DC heroes' powers. For instance, when facing Flash, who is super fast, Goku in Ultra Instinct might be able to match his speed or even anticipate his moves better. This could lead to a mutual respect between them as they test each other's limits.
Goku in Ultra Instinct mode is extremely powerful. He has superhuman speed, strength, and can dodge attacks effortlessly. However, Luffy also has his own set of amazing abilities like his Gear Fourth form which gives him enhanced speed and power. But I think Goku would win because his combat skills and power level are just on a different scale compared to Luffy.
A cool uq holder crossover fanfiction idea would be with 'One Piece'. The UQ Holder crew could sail on the Grand Line, encounter the Straw Hat Pirates, and get involved in their adventures. They might have to deal with the various pirates, sea monsters, and the strange islands. Or a crossover with 'Fairy Tail'. The magic of both worlds could combine in interesting ways, like UQ Holder's time - based magic mixing with Fairy Tail's elemental magic.
One idea could be a crossover with the Naruto universe. Goku with his Ultra Instinct could face off against Naruto in his strongest form. They might start as rivals but then realize they have a common enemy and team up. The story could explore how their different fighting styles and powers interact.
Todoroki might be another likely character. He has a complex power set and has been through a lot of emotional and physical growth. His struggle to control his two quirks could be a parallel to the control needed for Ultra Instinct. If he can master the balance within himself, it could potentially lead to the awakening of Ultra Instinct in him.
Maybe Goku gets mixed up in the events of the Injustice storyline. He could initially be confused by the alternate version of Superman who has gone bad. Goku, with his pure heart and Ultra Instinct, might try to bring the corrupted Superman back to the light. This could lead to some intense battles with the Injustice League as Goku tries to set things right.
First, understand the characters well. Know Goku's Ultra Instinct powers, his personality, his goals. Then, when choosing a crossover universe, pick one that has elements that can contrast or complement Goku's world. For example, if it's a magic - based universe, how would Goku's physical powers interact with magic? Keep the story focused on the main characters and their development throughout the crossover.
If Goku with Ultra Instinct crossed into the DC Universe, his powers would be very interesting. His speed could compete with the Flash. His combat skills and power would put him in a league with Superman. But the key difference would be how his Ultra Instinct operates. In a world full of superpowers and magic, his ability to react without thinking might be seen as a very unique power. It could also interact with the Green Lantern's ring energy in unexpected ways since it's all about willpower and Goku has a very strong will.