While Ranma's away the Chaos will play.
Part of the reason for this is that there are so few situations where someone makes an Inuyasha fusion and leaves enough of the NWC intact to really see how they interact with each other. I woke up thinking about this and know I won't ever write it. So where will whomever picks it up take this idea? Any other characters you want unchanged could simply not be in the area or others you want caught up in the mess from other series could have been staying in a Hotel or something.
The setting is an AU Nerima happening while Ranma and most of the NWC are off rescuing Akane from the Phoenix People.
In this setting Kiima made more trouble than cannon and so more people went after her to rescue Akane. Additions to the rescue party are Cologne, Ukyo, Konatsu, and Nabiki. The original group being Ranma, Ryouga, Genma, Shampoo, and Mousse.
Changes to those left in Nerima.
Tatewaki Kuno > Miroku
Yuka & Saiyuri > Kagome & Sango
Hiroshi & Daisuki > Inuyasha & Shippo
Principal Kuno > Seshomaru with both arms intact. Technically a half demon he may look and dress like Seshomaru (With sunglasses, the addition of his Hawaiian shirt under the Fur robes and the Pineapple tree on his head) but it didn't make anyone into a full demon.
Satsuki > Jakken only still obviously a Ninja.
Kodachi Kuno > Kaugra of the Wind. Without a Naraku to control and limit her what will Kodachi do with this change?
Soun would have become Naraku but Kasumi managed to purify the effects before it occurred.
Nodoka becomes a Miko similar to Kikyo's Sister but it doesn't alter her appearance, just her abilities.
Ryu Kumon > Koga of the Wolf Tribe
Ryouga gets lost after Akane is out of danger and ends up back in Nerima just in time to get caught up in this. Instead of becoming a recognizable character from Inuyasha it changes him into a Hanyo Pig Demon with 3 forms and complete control over the curse.
First being the visibly unchanged P-Chan only difference there is he can now talk in this form. (And he might not realize it)
Second being his normal "human" form it gets a duskier skin coloration looking like he's standing in the shade of a tree even in direct sunlight compared to the color it use to be.
Third form is a hybrid looking like a more athletically built Gamorean guard. It has all the right proportions from his Human form but clear pig features in the hands feet and head. He also ends up wearing only a loin cloth that leaves nothing to the imagination in place of all his clothes when he enters this form and also has Oni horns on his head so no one gets confused.
Pantyhose Taro also ends up with a Hanyo transformation similar to Ryouga only he can't speak in Cursed form and his Hybrid form has taken on aspects of a Shikima demon giving him both more tentacles and uses for them while muting the chimera appearance to something closer to human.
Of Ranma's and Nabiki's class most of the students end up taking on Villager roles while a few others take on other demonic ones. Miss Hinako is an exception. Due to her already changeable form being energy dependent whatever drives these changes can't find enough energy in her to do the same to her form. So she remains the same as always. If anything she gains memories of Rin.
Shortly after Akane's rescue but before Ranma's group gets back everyone listed wakes up with these changes. It has effected their memories. They know that InuYasha is a Manga + Anime and the characters memories are there obviously weaker than their real ones but still present. In addition they all find proper wardrobe and tools for their new memories and skills in their rooms as they wake up.
Nodoka doesn't realize there is any change to her until she goes to the Tendo Dojo. Really for her its little more than a change of clothing and choosing to carry a bow and quiver of properly prepared holy arrows along with the Honor sword. When she gets there Kasumi instantly realizes the change and convinces Nodoka to establish a true shrine with her, on the dojo grounds, in the empty corner just past the Laundry area. They end up having to purify a few of the more malignantly changed Furinken students before Ranma's group gets back. (It only causes them to return to normal) But seeing that some of the changes are beneficial they are not quick to insist on cleansing anyone. (Like making Principal Kuno more sane even if he's still a Hawaii nut.)
So how will this go? Where will you take the story? Will other series come into play? I already thought that Sailor Moon could easily manage cleaning up this mess before the group gets back but that doesn't mean she does it. So have fun and my list of changes is a suggestion but I really do think having Ranma's and Akane's friends become the core of Inuyasha's group is the best way to ensure there will be interesting interactions after they get back.

