The Soap of Happiness

 is the 120th chapter of the manga and the first chapter of the Waterproof Soap Arc.

Ryoga finds his way back to Furinkan with thoughts of Akane on his mind. He overhears two girls saying that if you write a letter in green ink, whomever you send it to will fall in love with you. Ryoga decides to write Akane a letter telling her how he feels and then heads to a bath house. Ranma and Genma are there since they broke the tub at home, and Akane is on the women's side talking to Shampoo. Shampoo tells Akane that she has some waterproof soap that will prevent her from changing into a cat when she gets wet. The soap slips out of Shampoo's hand and goes into the men's side where Ryoga finds it.

Ryoga Returns
Having found his way back to Furinkan yet again, Ryoga begins thinking that his love for Akane is what keeps causing him to return. He then wonders if he's truly happy just being Akane's pet, but quickly decides the outrightly isn't. As Ryoga begins to wonder just how he's meant to let Akane know his true feelings for her, two girls walk past and, whilst talking to each other, mention that they heard that people can't help but fall in love if you write a love letter in green ink. Ryoga finds the idea as nothing more than a girlish superstition, but can't stop himself from going to a craft store and buying some green ink anyway.

That rainy evening, Ranma and Genma are having to visit the local Sentō as the bath's been broken. Ranma soon notices some small boys chasing after P-chan, who's carrying a letter in his mouth. Ranma wastes no time in flicking some soap in P-chan's direction, which he slips on and tumbles into the hot water bath. As P-chan falls into the water, Ranma grabs the letter from his mouth and notices that it's addressed to Akane. He doesn't get chance to read it, however, as Ryoga swiftly takes it back before hitting Ranma on the head with his elbow.

Curious, Ranma takes the letter back and begins reading it out loud, but Ryoga hits Ranma again whilst reminding him that the letter isn't for him.

The Waterproof Soap
On the other side of the baths, Akane hears all the noise when she notices that Shampoo has walked in (in her cat form). After changing to her human form, Shampoo informs Akane that she'll never be a cat again and from today Ranma will belong to her. Understandably, Akane asks Shampoo what she's talking about, to which Shampoo shows Akane her recent purchase, Waterproof Soap! Shampoo explains that with this soap she can be covered in cold water, but will still remain in her human form.

As Shampoo gloats about how, with her cat form gone, Ranma will have no reason not to hate her. Unfortunately, Shampoo holds onto the soap too tight, causing it to slip out of her hand and fly into the male side of the baths. Meanwhile, Ranma continues to tease Ryoga about the letter when the soap causes Ranma to slip up before landing into Ryoga's hand. Ryoga takes the soap whilst noting that there is such a thing as karma. Back on the female side of the bath, Shampoo declares she must have the soap and so turns into her cat form. Akane tries to warn Shampoo about Ranma being over there, but it's too late and Ranma screams in horror at the sight of Shampoo's cat form.

Ryoga's Miracle
Some time later at the Tendo Dojo, Genma hands Akane the letter and claims he found it addressed to her at the Sentō. Ranma takes the letter and indirectly comments on how much of an idiot Ryoga is, he then begins reading the letter out loud, but Akane (most likely believing Ranma's teasing her) demands he just gives back the... But before Akane can finish, Ryoga appears, hits Ranma, and angrily declares that this is the last time Ranma will stick his nose into other people's affairs.

Akane is surprised that the letter is from Ryoga, which makes Ryoga more demanding Ranma return the letter. When Ryoga goes to grab the letter, however, Ranma trips him and Ryoga begins falling towards the Koi pond. Luckily, Ranma grabs Ryoga just in time, but the rock Ranma's leaning on gives way and the pair fall into the pond. As Ryoga falls into the water he despairs about how his love for Akane will now be for nothing.

Miraculously, when Ryoga emerges he's still in his human form whilst Ranma has turned into his female one. Ryoga then hits Ranma to check it's not a dream, prompting Ranma to hit Ryoga with a medium-sized stone in retaliation. Feeling the pain, Ryoga deduces that he isn't dreaming and is overjoyed to seemingly be free of his cursed form. Ryoga continues by deciding that he's now even if not superior to Ranma. He then takes his leave, not before telling Akane to read the letter from his heart whilst Ranma still wonders how Ryoga didn't change.

Akane looks at the letter, but it's gotten so wet that the ink is now unreadable. Shampoo, meanwhile, looks over the wall and grumpily thinks to herself that Ryoga used her soap, whilst Ranma becomes more infuriated at trying to figure out how Ryoga didn't change when he fell in the pond.

Cast in Order of Appearance

 * Ryoga Hibiki (human)
 * Akane Tendo
 * Ryoga Hibiki (P-chan)
 * Genma Saotome (human)
 * Ranma Saotome (male)
 * Shampoo (cat)
 * Shampoo (human)
 * Nabiki Tendo
 * Ranma Saotome (female)

Trivia

 * In the original Japanese version, the girls who Ryoga overhears talking about writing a love letter in green ink speak with "お嬢さま言葉" (ojou-sama) language, which is commonly used in anime and manga to describe some stereotypes, and originates roughly one hundred years ago from school girls in the Yama no Te district of the.