One idea could be that Tsunade is brought to the Justice League's universe through some sort of magical portal mishap. She could use her medical ninjutsu skills to help treat injured Justice League members, like when Superman gets hurt by a kryptonite - based weapon. Her tough - as - nails attitude would also make for some interesting interactions with Batman, who might be intrigued by her no - nonsense approach.
A possible fanfiction scenario could involve Tsunade being mistaken for an enemy at first by the Justice League. As they try to capture her, she resists, showing off her combat skills. Once they realize she's not a threat, they team up. Tsunade could then share her knowledge of chakra with the League, and in return, they could introduce her to their advanced technology. This could lead to some really cool combinations of powers and strategies in their future battles.
In a Tsunade and Justice League crossover fanfiction, perhaps Tsunade is summoned by the League because they've heard of her incredible strength. She could participate in a battle against a powerful villain, say Darkseid. Tsunade's ability to break the ground and cause massive destruction with her punches would be a great asset. And she could also teach the League some of her ninja techniques for stealth and evasion.
Tsunade would have an interesting dynamic with Wonder Woman. They are both strong female characters. Wonder Woman would likely respect Tsunade's leadership skills and combat abilities. Tsunade, on the other hand, might be impressed by Wonder Woman's god - like powers.
In a fanfiction, the Ghost Rider could form an alliance with Batman. Batman would be intrigued by the supernatural element that Ghost Rider brings. They could team up to take on villains who are using magic or other dark forces. Ghost Rider's powers of hellfire and his unearthly strength would be a great asset to the Dark Knight's strategic mind.
One idea could be that the Young Justice team gets accidentally transported to an alternate dimension where the Justice League has turned evil. The Young Justice members then have to figure out how to reverse the situation while also evading capture from their once - heroes. Another could be a time - travel plot where the Young Justice team travels back in time and teams up with the early days of the Justice League to stop a threat that was thought to be long gone but has resurfaced in their own time. A third idea is that a powerful new villain emerges who can only be defeated by a combined effort of the Young Justice and Justice League, but first they have to overcome their differences in fighting styles and leadership.
A cool plot could be a time - travel related crossover. The Young Justice team travels back in time and meets the younger versions of the Justice League members. They have to work together to stop a time - traveling villain from changing history in a way that would destroy the future. Or perhaps there's a magic - based crossover where a powerful sorcerer is causing chaos. The Justice League, which is more used to physical threats, has to team up with the Young Justice, some of whom have magic - related powers, to defeat the sorcerer.
Maybe a villain from the Justice League's rogues gallery teams up with an Avengers foe. Let's say Lex Luthor and Doctor Doom. They create a device that can swap powers between heroes from both teams. This leads to some really fun and chaotic situations. For instance, Captain America with the Flash's speed or Wonder Woman with the Hulk's strength. The two teams have to figure out how to work with their new, swapped powers and stop the villains.
In this type of fanfiction, the Predator could team up with the Justice League against a common enemy. For example, a powerful alien race that wants to conquer Earth. The Predator's skills in hunting and combat could be a great asset to the League. Aquaman could help the Predator adapt to the underwater environment if part of the battle takes place there. Green Lantern could use his power ring to create constructs to help in the fight against this new threat, while the Predator uses its stealth and weaponry.
A crossover with the Avengers. Picture the Justice League and the Avengers having to work together to stop an interdimensional threat. There would be clashes in leadership styles between Captain America and Superman, and also a lot of cool moments as different power - sets are combined to fight the enemy.
Well, a really cool crossover idea could be Fem Naruto using her chakra control skills to help Aquaman communicate better with his sea creatures. She could learn from him about the underwater world and in return, teach him some of her ninja stealth techniques. Also, Fem Naruto could work with The Flash. She might use her teleportation - like abilities (like when she uses her flying raijin) to keep up with The Flash and together they could stop a time - traveling villain.
A cool plot could be a race between The Flash and Gotenks. They both pride themselves on their speed, so it would be interesting to see how that pans out. Also, perhaps Vegeta could befriend Batman as they both have that brooding, serious personality. They could exchange combat and strategy tips. And what if the Dragon Radar was used by the Justice League to track down an energy source that was causing chaos in both universes?
One idea could be that an ancient, powerful enemy emerges that the Justice League alone can't handle. Supergirl, with her unique Kryptonian powers and different perspective, joins them. She might introduce some Kryptonian technology or fighting techniques that give them an edge. For example, she could have a device that can neutralize the enemy's energy - based attacks.