Yusuke's Rei - gun from Yu Yu Hakusho could be combined with Inuyasha's Tessaiga. For example, Yusuke could use his Rei - gun to enhance the power of Inuyasha's Tessaiga slashes. This would create a more powerful attack against demons. The combination of their raw power would be a force to be reckoned with.
One interesting plot could be that Yusuke from Yu Yu Hakusho gets transported to the world of Inuyasha. He teams up with Inuyasha and his group to fight a common enemy, like a powerful demon that is causing chaos in both their worlds. Yusuke's spirit energy could be a great asset in battles against the demons in Inuyasha's world.
Let's consider Seto Kaiba's technology - based cards and strategies in Yu - Gi - Oh. In a Bleach Yu - Gi - Oh crossover, his technology could be integrated with the scientific aspects of the Soul Society in Bleach. For instance, his holographic dueling technology could be used to create training simulations for Soul Reapers. And the psychic powers of some Yu - Gi - Oh characters could be used to communicate with the Zanpakutō spirits in Bleach. At the same time, the teleportation abilities of some Bleach characters could be used to quickly move around the dueling arenas in Yu - Gi - Oh, giving them an edge in battles.
In terms of character abilities, Naruto's Rasengan could be translated into a powerful card. When used in a duel, it could have an effect like destroying all the opponent's defensive cards on the field. And the Yu - Gi - Oh GX duelists' ability to summon powerful monsters could be used in a way that the Naruto characters see them as similar to summoning their own animal companions. They could learn from each other's summoning techniques.
Kagome's spiritual arrows could be enhanced by Grell's death scythe in a strange way. Maybe their combined powers could create a new weapon or a powerful blast that could defeat a very strong foe. Also, Shippo's illusions could be used to deceive the enemies, and Bardroy's explosives could be set off at the right moment to create chaos among the enemy ranks, which would give Inuyasha and the Black Butler characters an advantage in battle.
Inuyasha's demon blood could interact with the devilish powers in Highschool DxD. His berserker mode when his demon blood takes over could be enhanced or controlled by some of the devil's magic. On the other hand, the characters in Highschool DxD could learn from Inuyasha's group about fighting without relying too much on modern technology. For example, the simple yet effective fighting styles of Sango and Miroku could inspire some of the characters in Highschool DxD to improve their hand - to - hand combat skills.
Inuyasha's sword, Tessaiga, could be used in interesting ways in the Fruits Basket world. For example, if a Sohma is in trouble during their transformation, Inuyasha could use Tessaiga to protect them. On the other hand, the Sohma's zodiac animal abilities could assist Inuyasha in his battles. Like Kyo's cat - like strength and agility could help Inuyasha in a fight against a particularly fast demon.
I think Kurama and Kagome would be an interesting pair. Kurama, with his calm and intelligent demeanor, and his ability to use plants and nature - based powers in combat, could learn a lot from Kagome's knowledge of spiritual powers and the Sacred Jewel. Kagome, on the other hand, could be intrigued by Kurama's complex past as a demon - turned - good. They could exchange ideas about how to deal with demons and use their respective powers more effectively. And their more gentle personalities compared to some of the other characters in their respective shows could lead to some really interesting character - development - focused interactions.
Well, perhaps the Sacred Jewel from Inuyasha somehow gets linked to the Spirit World in Yu Yu Hakusho. Kagome and Inuyasha follow the strange energy trail to the Spirit World. There, they meet Yusuke and Kuwabara. They find out that a powerful spirit in the Yu Yu Hakusho world is corrupted by the dark energy of the Sacred Jewel fragments. So they all have to work together to purify the spirit and restore balance to both worlds. The differences in their fighting styles, like Inuyasha's swordsmanship and Yusuke's martial arts - based spirit attacks, would make for some cool battle scenes.
Archive of Our Own (AO3) is also a great place to find such fanfiction. There are many well - written and creative 'yu yu hakusho crossover' stories there. The tagging system on AO3 makes it easier to filter and find the specific crossovers you're interested in.
One common theme is power exploration. Since Hiei is a powerful character, fanfictions often explore how his powers interact with new elements in the crossover. For example, in crossovers with other supernatural worlds, how his demon powers compare or combine.