Well, one way is to have a portal that connects the two worlds. Characters from both sides accidentally pass through it. Then they have to figure out how to get back while dealing with the problems in the other world.
Writers often start with a what - if scenario. What if Naruto was born in the Mass Effect universe? How would his life be different? They use this as a starting point to blend the storylines. They also consider the political aspects of both universes. The complex politics in Mass Effect like the council races and the ninja village politics in Naruto. By making characters interact with these political systems, they merge the two universes' storylines.
The blending could occur with the technology and powers. In Naruto, there are various jutsus and kekkei genkai. In Mass Effect, there's biotics and advanced technology. A fanfic could make it so that the shadowy elements in both worlds are related to a new form of power. For example, a shadow - based biotic power that is similar to the shadow - based ninjutsu in Naruto. This new power could be something that is being hunted or coveted by different groups in the story.
The characters from both universes interact in various ways. The harem aspect comes in as Naruto's charm and unique abilities attract characters from SAO. The fanfic might also blend the cultures of the two worlds. For instance, Naruto's respect for his comrades from the ninja world could influence how he forms relationships in the SAO harem. There could be training arcs where Naruto teaches the SAO characters some ninja techniques, or vice versa, the SAO characters introduce Naruto to new virtual world strategies. This creates a rich blend of the two universes.
Well, a 'Naruto Godlike RWBY Fanfic' blends the two universes in multiple ways. Firstly, the story often has Naruto as an outsider who brings new knowledge and combat techniques. His use of chakra and elemental jutsus can be a huge advantage in the RWBY world. Secondly, the cultures are combined. The ninja culture from Naruto, with its clans and hierarchies, can interact with the RWBY culture of Huntsmen and Huntresses. This can lead to interesting scenarios where Naruto might train RWBY characters in ninja ways or vice - versa. Also, the fanfic might play with the idea of Naruto's godlike powers being a result of some sort of Remnant - related phenomenon, thus deeply connecting the two universes.
In many fanfics, the settings are combined. You could see the Hidden Leaf Village in the middle of Hyrule, or vice versa. The cultures also mix. The honor - based system of the ninja in Naruto could be applied to the characters in Zelda, or the magic system of Zelda could be introduced to the Naruto world. This creates a whole new and exciting world for the readers. It's really interesting to see how the different power dynamics, social structures, and technologies from both universes interact and change in these fanfics.
The storylines could be blended by having a shared goal. Suppose there is a threat that endangers both the Naruto world and the Sekirei world. It could be a new, powerful and evil force. Characters from both series would then have to work together to defeat this threat. Along the way, they would learn about each other's worlds, powers, and cultures. For instance, Naruto characters could teach Sekirei about teamwork in the context of a ninja squad, while Sekirei could show Naruto characters their unique way of bonding with their Ashikabi.
They often blend the two universes by having characters cross over. For example, Naruto could end up in the 'Dragon Ball Z' world and start learning about ki and fighting Saiyans. Or a 'Dragon Ball Z' character could visit the Hidden Leaf Village.
To blend their universes well, start with a believable crossover event. For example, a mysterious portal could open between the two worlds. Then, focus on the characters' reactions. Naruto would be curious and eager to explore, while Zero Two might be more cautious but also intrigued. Their different personalities can drive the story as they learn about each other's worlds.
Typically, it blends the universes by having characters cross over. For example, Naruto might end up in the Star Wars galaxy or vice versa with Revan in the Naruto world. Their powers are then compared or combined. Naruto's chakra system could be related to the Force in some ways.
Some fanfictions blend the two universes by introducing elements of one into the other. For instance, the Death Note's rules might be applied in the Naruto universe. So a character in Naruto might get hold of a Death Note - like object with similar powers, and then the story explores how that changes the Naruto world's balance of power and relationships. It can also involve characters from Death Note trying to understand the ninja way of life in Naruto, which is full of loyalty, honor, and complex clan politics.