Of course, in the end, it was really Ryoga's fault.

Our hero Ranma was on his way to school with Akane, at the end of the manga, and just a moment too late, he and Akane saw a vague and indistinct shape, mostly invisible, appear in front of them, and felt a sudden surge of danger.

That was just a moment before Ranma was knocked into the canal, hard. When she got out, it was already upon her again, and she could barely see it. Akane was of course yelling worriedly, having been knocked aside by the invisible monster.

The monster disappears completely again, and as soon as it re-appears, it hits Ranma even harder, knocking her konpaku out of her body.

"Now I can finally kill you! Prepare to die, Ranma!" and the monster, which looked like a huge humanoid pig with a giant white mask and a hole through it's chest, grabbed and snapped the chain attaching Ranma to her body.

Ranma is weak, unable to move or breathe properly in konpaku form, has no ki, and the monster is laughing and bragging about finally defeating her. Akane can't seem to see it and has come down to Ranma's body by the side of the canal, and is yelling and shaking it.

The monster, which reveals itself to be Ryoga, grabs Akane, and starts yelling that she belongs to him, now that he defeated Ranma. Ranma can't let it hurt her, and attacks it as best she can, causing it to drop Akane and focus on her. The monster states that it will destroy her, and changes into a pig mask headed missile that spins and charges at Ranma.

In her panic, Ranma's spiritual energy rises, and she's able to barely dodge the attack. Ranma leads the monster away from Akane, but is unable to damage it with her attacks, nor is the monster fast enough to hit her, as her speed seems to be slowly returning to normal, at least normal when she isn't boosting her speed with ki. Ranma can tell that she's going to get tired sooner than the monster though, but she is successfully leading it around and keeping it too angry to think straight.

Then Ranma slips into an alley to climb up to the rooftops with some stacked boxes, unfortunately, or perhaps fortunately, she runs into a cat. In her paniked state, the neko-ken is triggered almost instantly. But it doesn't behave normally in her konpaku form, Ranma's chain of fate disappears, her eyes become slatted, her teeth sharper with her k-9's becoming fangs, her ears shift up on her head, and become triangular cat ears, covered with fur the same color as her hair, and she grows a tail the same color as her hair, her nails become claws, and her outfit changes to a modified shinigami outfit, a white hakama with a belt, and a hole in back for her tail, and with open toed sandals to show her claws on her toes. Ryoga-hallow enters the alley, and is surprised by the change, but not for too long, as he's heard about the neko-ken. He attacks Ranma, but that's not exactly a good idea.

Spirit claws flash out and destroy his mask, the gates of hell open up, and Ryoga-hallow is taken away. Neko-Ranma is confused an irritated with her current state, goes off in search of Akane, finds her holding her body and crying over it, shaking her and yelling at her to wake up. Neko-Ranma goes back to her body, mostly by accident trying to get in Akane's lap.

Ranma wakes up, unable to remember what happened since she saw the cat, and very pleased that she seems to be alive again. Akane is happy too that Ranma has woken up, but is worried the invisible monster is still around, Ranma is too, and tells Akane that the monster was Ryoga, and that she'd had an out of body experience and was unable to beat him or even damage him, and the last thing she remembers is seeing a... well, she can't say it, but Akane gets the idea, and is worried about Ryoga, saying they have to change him back.

They got to school, getting there a bit late, and Ranma freaks out when she discovers during break that she can't change back. On top of that, Ranma is now seeing ghosts all over the place, ones that Akane can sense the presence of, but not see or hear. Hinako-sensei prevents them from leaving school until the end of the day, even to try and figure out how Ranma's curse was locked, so they end up waiting till the afternoon to go to the Nekohaten to demand from Cologne what is going on.

Cologne apparantly knows a bit about Hallows. And after she gets the story out of Ranma of her experience, she realizes that Ryoga is dead, and became an evil spirit, and may or may not be still at large, depending on if the neko-ken defeated him or not. Even if it didn't, more Hallows will likely come after Ranma who is now displaying high spiritual energy, which Hallows like to consume. On top of this, the Jusenkyo curse is a complete transformation, down to the soul, but the magic is only attached to the body, and only can stay attached to a living body, since Ranma died in female form, she's trapped until they can get some Nanniichuan water, which is usually an empty pool which only fills up a few times during the year, and they can repeat the process that got Ranma stuck, trapping her in a male form instead, which would be a cure.

In order to deal with the Hallows that will likely be coming, Cologne decides she'll take Ranma alone, to Karakura town, where they can get some spiritual supplies from the Urahara shop, which Cologne had heard about, including some anti-Hallow weaponry.
The group arrives just when Ichigo is about to start his training to become a shinigami with his own power. Urahara recognizes that Ranma has partially become a shinigami, and her assistance in saving Rukia is requested, and training offered in exchange for the help.

They manage to expel Ranma from her body, revealing the same costume as neko-Ranma, but without the cat features, Urahara places Ranma's body in protected storage, and begins training her while Ichigo is in the pit. Inside Ranma's soul, Ranma doesn't encounter a zanpakutou, but does encounter the neko-ken, which takes the form of a pure white kitten with glowing pink eyes which chases her around merrily, while Ranma screams for her life and runs around madly. This continues for a while as Ranma builds up enough courage to start thinking more clearly, and realizes the kitten could be the form of her zanpakutou, and tries to talk to it while still running, but it can't talk.
Finally, Ranma manages to calm down enough to let the kitten come to her, even though she's still terrified of it, realizing that it probably can't hurt her, since it's part of her soul, and it's so small and she's pretty big now. The kitten rubs up against her a bunch until Ranma finally reluctantly relents and pets it.

When Ranma does this, she's assaulted with memories of all the times she was under the neko-ken, which helps her overcome the fear, and she merges with the kitten, awakening in the cat featured form with a burst of spiritual energy.

Urahara realizes that Ranma's zanpakutou is abnormal, due to the neko-ken. Ranma's tail is noticed to have a ribbon on it that has the konsoh symbol on it, and Ranma's claws are her zanpakutou blade, he figures out that Ranma is competely merged with her zanpakutou as far as her spiritual body goes, but she still has not mastered it mentally or spiritually.

While Urahara is training Ichigo, Ranma trains under Yoruichi with Sado and Inoue. Ranma is terrified of the talking cat, and is easily bossed around by the amused Yoruichi, but does manage to make some progress with mastering her basic claw attacks and even masters her feline ajility, senses, and flash step, much to Yoruichi's surprise.

During this training, Cologne returns to tell everyone Ranma's on a training trip to master a new technique she told Ranma about that she'll need to recover her male form, and that they won't be able to find her. She only tells Akane and Shampoo the truth of the matter, giving them both weapons she bought at the Urahara shop, a pair of clubs for Shampoo, and a pair of gloves for Akane, that will allow them to defeat lesser Hallows without spiritual techniques in case the Ryoga hallow is still at large. She also brings back the dead body of Ryoga, which she found out he'd killed himself since he thought Akane had married Ranma at the failed wedding, which he wandered away from before it was over.
Ranma finds out about hell and soul scociety from the workers at Uruahara shop, and is upset that Ryoga went to hell, and finds out that it was probably because of using his pig form to spy on Akane and trying to rape Ranma when she was in a disguise pretending to be his 'long lost fiancee', as well as blaming all his problems on others, even when they were his own fault, and trying to kill Ranma so many times. She also suspects he may have done worse things she doesn't know about.

The group goes to soul scociety. Mayuri searches after Ranma he heard about as she's a 'wonderful unique specimen', but Ranma avoids the creepy freak, who runs into Inoue and Ichida instead as the regular Bleach.

Ranma ends up getting to the tower first. She's stopped from saving Rukia by Soi Fong, who nearly kills her, placing her marking technique on her and treatening to kill Ranma with it, then dragging Ranma off to be interrogated. Ranma explains that they were taken by Yoruichi, sent by Uruhara, to rescue Rukia, and that she doesn't know much else, and explains the circumstances in which she became a shinigami, except for the part about being origionally a boy, which she's reluctant to explain since she doubts she'll be believed. (Inoue, Chad, and Ichida don't know either, although Ichigo and the Urahara shop people and Yoruichi know)

Soi Fong is upset to find out about Yoruichi, and goes off to search for her, dragging along Ranma to track Yoruichi's scent. But this isn't before they show Ranma the 'dead body' which Ranma recognizes for them as an illusion, causing Soul Scociety to find out about the plot sooner. They don't manage to find her until Yoruichi is training Ichigo to fight Byakuya, at the secret base. Yoruichi defeats Soi Fong, and doesn't explain herself, simply saying that Soi Fong can continue to fight them, or she can help them keeping an eye on Ichigo's training while Yoruichi trains Ranma.

Ranma is shocked to find out that Yoruichi has a human form, although she'd already figured out by scent that Yoruichi is female. Yoruichi has theorized that Ranma can achieve Bankai by going through the training Yoruichi went through to gain her cat transformation, which is a difficult and risky training which can kill the person, but allows them to master their inner animal.

Ranma manages to achieve bankai, and can now transform to multiple states in between human and feline, although unlike Yoruichi, Ranma's feline form is white and smaller, and Ranma keeps her clothes when in more human of states, the clothes transforming with her into just the tail ribbon in fully furred forms. Ranma gains the ability to launch her claws as a bunch of concentrated reiatsu blades as a ranged attack which has power based on her focus, concetration, and the amount of reiatsu put into it, and is meant for attacking large groups of opponents. Ranma's shikai is changing into a more powerful and faster hybrid form which regenerates from injuries and is resistant to tricks and illusions created by zanpakutou and kidou. Ranma's bankai changes into an even more powerful version of her shikai, which has very high spiritual pressure, so she's very hard to cut, and has better strength, speed, senses, and regeneration than the shikai, and also has glowing red eyes, white fur, and a split ended tail which allows her to control her opponent's movements, although it only slows down opponents with spiritual energy around her own level or slightly higher, and can't affect those with significantly higher spiritual pressure, nor can it control an opponent's spiritual energy, only the movements of their body. It actually allows her to control only spiritual entities and corpses, not living beings. Ranma also learns that the name of her zanpakutou is nekomata, and that it's been a zanpakutou of a famous shinigami who died, and Ranma is the reincarnation of, although Ranma's bonding with it is very different, and Ranma is very different from her past incarnation, and Ranma is no longer a normal shinigami.

Well, that's about as far as my idea gets. Ranma would go back with everyone, and by then Urahara would have made her a gigai of Ranma's male form, which Ranma uses temporarily instead of her real body. Ranma is weirded out tough, because she finds that it's very weird to have a female soul and a male body and ki. Ranma has her own adventures fighting Hallows with Akane and Shampoo while everyone else is dealing with the Bounts I suppose...