Inuyasha's physical strength and combat skills with his sword could be combined with Zatch's magical attacks. For example, Inuyasha could use his speed to get close to an enemy while Zatch casts a spell to immobilize or weaken the foe. Then Inuyasha could deliver a powerful strike with Tessaiga. Another way is that Zatch could use his magic to enhance Inuyasha's attacks, like making Tessaiga's wind scar even more powerful or giving it additional elemental properties.
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.
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 idea could be that Inuyasha's Tessaiga and Zatch's spell book somehow get switched. This would lead to Inuyasha trying to figure out how to use Zatch's magic while Zatch has to deal with a powerful and strange sword. Another plot could involve a common enemy that forces Inuyasha and Zatch to team up. Maybe a demon from Inuyasha's world has found a way to cross over into Zatch's world and is causing chaos, and only by combining their powers can they stop it. A third plot could be a more comical one where Inuyasha and Zatch meet by accident and at first think the other is an enemy but then slowly become friends through misunderstandings and shared adventures.
If Naruto was in the Splatoon world, his Shadow Clone Jutsu could be used in interesting ways. He could send clones to cover more ground during an ink battle, confusing the enemy. And for the Inkling's part, their ability to swim in ink could help Naruto move around in ink - filled areas more easily. They could also use their ink guns to provide cover for Naruto while he attacks up close.
Well, if Izaya from Durarara and Shikamaru from Naruto were to team up, Izaya's intelligence in manipulating people and Shikamaru's strategic thinking could create some really devious plans. Shikamaru could use his shadow - binding jutsu to physically restrain opponents while Izaya uses his words to mislead and confuse their enemies. Another example is if Celty's shadow powers were combined with Naruto's chakra - enhanced strength. Naruto could use Celty's shadows to extend his reach in battle, like creating shadow - arms that are empowered by his chakra.
Naruto's ability to use chakra and his shadow clone jutsu could be combined with the Ninjago ninjas' elemental powers. For example, Naruto could create shadow clones to help Kai with his fire - based attacks in a battle.
The sharingan ability from Naruto's world could be used in an interesting way with the Voltron technology. For example, a character with the sharingan could quickly analyze the weak points in the Galra's defenses or the mechanisms of the Voltron lions themselves, allowing for more efficient repairs or strategic attacks. And Voltron's ability to form into a giant robot could be used as a cover or a platform for Naruto characters to perform their long - range jutsus from a safe vantage point.
Naruto's ability to use chakra could be combined with Batman's gadgets. For example, Naruto could use his chakra to power up some of Batman's energy - based weapons. Batman's detective skills could help Naruto in his ninja missions in the Naruto world. He could analyze the enemy's patterns and strategies better. Also, Naruto's shadow clone technique could be used for reconnaissance in Gotham, while Batman's stealth could be applied in the Hidden Villages for spying on potential threats.