One idea could be that Sephiroth somehow gets transported to the feudal era of Inuyasha. He might initially be seen as a great threat due to his power. But as the story progresses, he could form an unlikely alliance with Inuyasha and his group against a common enemy, like a powerful demon that is even more menacing than any they've faced before.
Perhaps there could be a scenario where Sephiroth's powers are affected by the magic in Inuyasha's world. His Materia may not work as expected, and he has to learn to adapt and use the local magic or spiritual powers. Inuyasha and his friends could be both intrigued and cautious of Sephiroth, not fully trusting him but seeing the potential of his power in their battles.
Inuyasha would probably be very wary of Sephiroth at first. Inuyasha is used to dealing with demons and his own set of problems in his world. Sephiroth's otherworldly power and cold demeanor would make Inuyasha see him as a potential threat. He might even attack first out of instinct.
One idea could be that Sakura, with her medical ninjutsu skills, ends up in the Feudal era of Inuyasha. She could help treat the wounds of the villagers who are often attacked by demons. Inuyasha might be initially suspicious of her strange powers but gradually come to respect her as she proves her worth in battles and in healing the injured. For example, when Inuyasha gets seriously injured in a fight against a powerful demon, Sakura's medical skills could be the key to saving him, which would change his view of her.
One idea could be that Sephiroth somehow gets transported to the RWBY world. He might initially be seen as a threat, but then the characters realize he has knowledge that could help against a new, powerful Grimm. For example, his combat skills and his understanding of magic - like materia in his world - could be adapted to the Dust - based magic in RWBY.
One idea could be an Inuyasha and Naruto crossover. Picture Inuyasha in the Hidden Leaf Village, his sword skills and demon powers causing quite a stir among the ninja. Another could be a crossover with Harry Potter. Inuyasha at Hogwarts, trying to figure out magic while also dealing with his own demon - slaying business. Maybe he'd have some interesting interactions with the magical creatures there.
One idea could be that Ichigo from 'Bleach' somehow gets transported to the world of 'Inuyasha'. He might meet Inuyasha and they could team up to fight a common enemy, like a powerful demon that has somehow gained the powers of Hollows from 'Bleach'. Their different fighting styles would make for an exciting combination.
One idea could be to cross Inuyasha with a modern detective story. Inuyasha's keen senses and combat skills would be useful in solving mysteries in a modern city. Another idea is to cross him with a magical school setting, where he has to learn new types of magic along with the students. Maybe he could also be crossed with a post - apocalyptic world, and his survival skills would come in handy for him and the other survivors.
A cool plot could be that there's a tournament across different anime worlds, and Inuyasha and Naruto are chosen to represent their respective worlds. Along the way, they discover similarities in their pasts, like both having some form of demon - related heritage (Naruto with the Nine - Tails and Inuyasha being a half - demon). They also exchange combat techniques. Naruto teaches Inuyasha how to better use chakra control in his attacks, and Inuyasha shows Naruto some unique sword - fighting skills.
A possible plot could involve the Hollows from Bleach somehow making their way into the Inuyasha universe. Inuyasha and his friends would have to team up with Ichigo and the Soul Reapers to fight them. This would create a really interesting dynamic as the different fighting styles and powers collide. The Hollows might also target the demons in Inuyasha's world, seeing them as a new source of power or prey.
One idea could be that Inuyasha gets transported to the Ouran High School world. He'd be this wild and rough - around - the - edges character in a posh, refined school setting. Maybe he mistakes the Host Club for some sort of demon - like group at first and tries to fight them. Another plot could involve a character from Ouran getting dragged into Inuyasha's feudal Japan world and having to adapt to the lack of modern conveniences and the presence of demons.
A really unique plot could be a situation where the tailed beasts in Naruto are related to the powerful demons in Inuyasha. For instance, the Nine - Tailed Fox could have a connection to a major demon in Inuyasha's world. This discovery could lead to a journey where Naruto has to travel through the Inuyasha world with Inuyasha and Kagome to find out the truth about this connection and how it can help or harm their respective worlds.