Well, in a My Hero Academia Undertale crossover fanfiction, the characters' abilities could combine in really interesting ways. For example, Deku's One For All could potentially merge with Sans' ability to dodge attacks effortlessly. Deku might gain the power to not only have super strength but also be able to anticipate and avoid attacks like Sans. And Ochaco's zero - gravity power could interact with the gravity - manipulating powers in Undertale. Maybe she could use her power to counteract some of the strange gravitational effects in the Underground world.
Uraraka's zero - gravity Quirk could work well with a Stand like The World. She could make objects weightless and then use The World's time - stop to position them in the perfect place for a powerful attack. For example, making a large boulder weightless, stopping time, and then moving it right above an enemy before time starts again.
Genos' robotic enhancements and Kirishima's hardening quirk could create an interesting combination. Genos could provide Kirishima with some technological upgrades to his hardening ability, making him even more indestructible. On the other hand, Saitama's speed could be combined with Iida's engine quirk to create a super - fast movement ability that could outpace almost any villain.
If we consider the healing abilities in both games, the bugs in Hollow Knight that can heal the Knight could teach Toriel about new ways of healing. Toriel could then use her magic in combination with these new techniques. The Knight's ability to climb walls and ceilings could be combined with Napstablook's ability to float. They could create a new form of movement that allows them to access areas that were previously unreachable. And the magic attacks of the Undertale characters, like Muffet's spider webs, could be enhanced by the magic of Hallownest, making them more durable and effective in combat.
In a crossover fanfiction, the combination of powers could be quite complex. Let's take the idea of Uraraka's Zero Gravity Quirk and the power of the Float - Float Fruit from One Piece. If Uraraka were to somehow gain the ability of the Float - Float Fruit, she could manipulate gravity in even more extreme ways. She could make objects or people not only float but also move them around in mid - air with greater precision. Similarly, if Zoro were to be introduced to the concept of Quirks, his three - sword style could be enhanced with a Quirk that gives his swords special properties, like the ability to cut through any substance, even intangible ones like some Quirk - based attacks.
The quirks in My Hero Academia are often very physical and unique to each individual. In a crossover, Uraraka's zero - gravity quirk could be used in space battles in the Star Wars universe. She could disable enemy ships by making them weightless. On the other hand, the Force abilities in Star Wars, like mind control and precognition, could give the My Hero Academia characters an edge in combat. For example, Todoroki could use his ice quirk in combination with a Jedi's precognitive ability to anticipate his opponents' moves and freeze them in place before they can act.
One way is to have a character with a strength - based Quirk in My Hero Academia combine it with 'The Gamer' skill of stat - boosting. For example, if a character has super strength, they could use 'The Gamer' ability to boost their strength even further for a short period. Another way could be for a character with a speed - related Quirk to use the 'Gamer' dodge ability to make their movements even more unpredictable.
Imagine if Spider - Man had Naruto's chakra control. He could use his webs in a much more precise and powerful way. He could also potentially use chakra to enhance his already amazing acrobatic skills. On the other hand, Naruto characters could learn from the strategic thinking of characters like Captain America. Naruto himself could use some of Cap's leadership skills to better lead his ninja teams in battle. And Sasuke could use some of the stealth and infiltration techniques that Black Widow is known for.
One potential plot line could be that the villains from My Hero Academia somehow find a way into the Undertale universe. They start causing chaos and trying to take over the Underground. The heroes from My Hero Academia then team up with the friendly monsters in Undertale to fight back. Along the way, they learn about each other's powers and cultures.
The heroes in My Hero Academia would be in awe of Spider - Man's abilities. His ability to climb walls and swing from buildings would be something new to them. They might try to incorporate some of his moves into their own fighting styles. Midoriya would look up to Spider - Man as another symbol of hope, just like All Might.
Obviously, Saiki K himself would be one of the main characters. And from My Hero Academia, Izuku Midoriya could be another main character. Their interactions would be really interesting, like Midoriya being in awe of Saiki's powers and Saiki being a bit annoyed by Midoriya's over - enthusiasm.