Here is a story Idea/Challenge for any writer to use.
Take a storyline from the manga telling it from a first person point of view while making it into a horror story.
Bonus points for altering it as little as possible.
Bonus points for keeping the characters in character.
This idea came to me from reading the manga Scary Book by Kazuo Umezu in which the very first story is about a girl who spends a lot of time looking into a mirror and her reflection comes to life and tries to take over her life. This has several parallels with the mirror clone storyline in the Ranma ½ manga. In the Ranma manga a beautiful young woman spent most of her life gazing into the mirror and died unloved, her spirit possessed the mirror and takes the form of the person to look in to the mirror. In both stories the mirror reflection causes a lot of trouble. There are other parallels between the two stories such as both reflections want to find love, both places with mirrors are called Mirror Mansion, both mirrors break, etc. Takahashi could have easily made it into a horror story. This is true for many of the story arcs like Ranma losing his strength from Ranma's view point, Akane's view point of being turned into a doll while her body is trying to kill Ranma, or Ranma nearly being dragged to the bottom of the sea by a cursed swim suit, etc.
Even though I mentioned the mirror clone story line the arc I'd most like to see this done to is the Koi Rod Arc told from Ranma's point of view. We are told barely any of his thoughts. You could have Ranma wondering what is wrong with himself with him falling in love with Ryoga and then tell the story where he is falling in love with him. Then have Ranma angsting about what happened under its effects afterwards things like trying to kill Akane, wanting to marry Ryoga, kneeling in a grave praying for Ryoga's happiness while waiting for him kill him, etc. Another way to go about telling it would be for Ranma to be fully aware but unable to stop himself from doing the stuff. With part of his mind silently screaming things like no don't do that or when he (she really) was kneeling and praying for Ryoga part of her was silently screaming to move, get up, fight back, do something anything, etc.