The key is to find common elements. For example, both universes have different forms of power. In Naruto, there are chakra - based powers, and in Mass Effect, there are biotic and tech powers. The mind - control aspect could be related to a new form of chakra or a corrupted biotic power. Characters from both universes could be brought together through a mysterious portal or some sort of interdimensional rift.
To blend the two universes well, you could start by establishing some common ground. For example, both have elements of mystery and danger. You could have the magic from the Harry Potter universe interact with Slenderman's spooky abilities. Maybe Slenderman's presence distorts the magic around him in Hogwarts, causing strange things to happen. Another way is to introduce a crossover object or character that belongs to both worlds in a way.
In 'Mass Effect mind control fanfic', it often works through biotic powers. For example, a character with extremely strong biotics might be able to project their thoughts into another's mind and manipulate their actions. It could also be related to some sort of new technology. Maybe a device is discovered that can send out electromagnetic waves that interfere with a being's neural pathways, allowing for mind control.
The cultures of their universes can be blended. Naruto's world has a strong sense of community and loyalty within the ninja villages. Sephiroth's world might have different values. By having the characters interact and learn from each other's cultures, like Naruto teaching Sephiroth about friendship and she teaching him about some unique aspects of her world's technology or magic, it can blend the universes well. Also, the settings can be merged. Maybe there's a place that exists in both universes but in different forms, and they have to go there together.
One idea could be that a character from Mass Effect somehow gets transported to the Naruto universe and has the ability to mind - control certain characters, leading to the formation of an unexpected harem. Maybe they use this power to bring together ninjas with different skills to form a unique team.
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.
One way is through character interactions. For example, Shepard could team up with Ruby and they could share their combat experiences. Shepard's military training from Mass Effect and Ruby's Huntsman skills from RWBY could create interesting battle strategies. Another aspect could be the technology transfer. Maybe the advanced tech in Mass Effect like biotics could be introduced to RWBY's world, causing a stir among the characters there. Also, the cultural differences between the two universes could lead to some great storylines. The more rigid military structure in Mass Effect compared to the more free - flowing world of RWBY could lead to clashes and reconciliations.
One way could be through a magical or technological device. For example, a portal could be created that links the Naruto universe and the Star Wars universe where Jedi exist. This would allow characters from both worlds to interact.
The two universes can be blended well by focusing on the values of the characters. Both Naruto and the characters in Case Closed have a strong sense of justice. You can build a story around this common value. Maybe there is a conspiracy that threatens the justice system in both worlds. The ninjas and the detectives would then come together to uphold justice. This could involve Naruto using his rasengan to break through physical barriers during investigations, while Conan uses his sharp mind to figure out the motives behind the conspiracy, which are often related to power struggles or revenge, just like in his own world.
In some 'Mass Effect mind control fanfic', it could focus on the asari. Since they have strong biotic abilities, a story could be written where an asari with a unique biotic - based mind - control power tries to take over the Citadel. She uses her power on various species' ambassadors to gain control of key decision - making processes. However, a group of resistance fighters, including some of our favorite Mass Effect characters, band together to stop her.
One way is through power systems. The biotics in Mass Effect and the chakra in Naruto can be related. Maybe a character in a fanfiction discovers that biotics are a form of chakra or vice versa. Also, the different races in Mass Effect and the clans in Naruto can interact in terms of politics and alliances. For instance, the Uchiha clan could form an alliance with the Salarians based on their shared intelligence and strategic thinking. And the stories can also use the different settings, like having a battle take place on a Mass Effect planet but with Naruto - style combat techniques.