Well, it could be through a portal. Maybe a scientist in the Naruto world accidentally creates a portal that sucks in the Green Goblin from his own world. This simple concept can start a whole new adventure where the two worlds collide.
Well, it can combine them through magic. For example, Soviet wizards might have developed spells that are unique to their environment, like spells to deal with the cold. And these spells could be introduced to the Hogwarts students in the fanfiction.
It combines the two worlds by using the elements of the Harry Potter universe as the basis for the stock market. For example, stocks could be based on Hogwarts houses, with their different values and reputations affecting the market. Magical items like wands and potions can also be turned into stocks. The characters' actions and relationships can influence the market too, just like in the real world where businesspeople's decisions affect stocks.
Typically, it combines the two universes by having characters interact. Naruto characters might find themselves in the magical world of Winx Club or vice versa. They would then have to adapt to the new environment and rules. But as for the 'lemon' part which might not be suitable, we should focus on the positive aspects of this combination like how Naruto's combat skills can be compared and contrasted with the Winx Club's magical battles.
The combination can be achieved by having the Titanic be a part of a hidden quest in the Fairy Tail world. For instance, there could be a powerful magical artifact on the Titanic that the Fairy Tail guild is after. So, the characters board the ship with the aim of retrieving it. Along the way, they face the challenges that come with the Titanic's voyage, like the class differences among passengers, the approaching iceberg, and of course, the inevitable sinking. Their magic then comes into play to either solve these problems or at least make their situation better.
Often, it combines them through crossovers. For example, a portal could open between the Naruto universe and Shinji's world, allowing characters to travel between them.
Well, it could start with a magical portal that transports Naruto to the Snow White world. The portal could be opened by some sort of forbidden jutsu gone wrong.
It combines elements by bringing together the unique aspects of each franchise. Naruto has its ninjutsu, chakra system, and complex character relationships. Rick and Morty has its wacky science, interdimensional travel, and dark humor. In fanfiction, they might have Naruto using a portal gun or Rick trying to understand chakra. Simple as that.
The combination in 'Watch Dogs MLP Fanfiction' is often through the concept of displacement. A character from Watch Dogs suddenly finds themselves in Equestria or vice versa. Then they start to interact with the elements of the new world. The Watch Dogs' tech - savvy characters might try to understand and even use the magic in MLP as if it were a new form of technology. And the ponies would be exposed to advanced technology which is completely foreign to them. This creates a lot of interesting scenarios for storytelling.
The settings can also play a part in combining the cultures. Hogwarts could be seen in a new light when Hindu elements are added. For example, there could be a special hall in Hogwarts dedicated to Hindu deities where students can go for spiritual guidance. This would be a unique blend of the Western - style magical school and Hindu religious elements, creating a whole new world within the fanfiction.
One way is through the use of similar themes. Both Naruto and Mirai Nikki have elements of survival. In the fanfiction, this could be shown by characters in the Naruto world having to use the future - predicting aspect of the Mirai Nikki concept to survive battles or political intrigue in the Hidden Villages.