The Legendary Moxibustion of Evil

 is the 125th chapter of the manga and the first chapter of the Ultimate Weakness Moxibustion Arc.

Ranma causes Happosai to get beaten up on one of his daily panty raids and Happosai pays him back by placing a hot ember on his back. The next day on the way to school, Kuno tries to fight Ranma, but Ranma's punches do nothing to Kuno. Kuno beats Ranma easily, followed by a little boy punching Ranma's lights out.

Happosai's Wrath
Whilst walking down the streets of Furinkan, Ranma notices Happosai being chased by a group of women after being on one of his usual panty raids. Ranma decides to throw his Pork bun at Happosai, which distracts the old lecher long enough for the women to catch up and subsequently beat him up as Ranma walks away.

That evening at the Tendo Dojo, when Happosai returns he immediate goes to Ranma and tells him that for taking his one moment of happiness, he shall pay dearly. Happosai then declares that he shall burn Ranma with the power of Moxibustion and throws something in Ranma's direction. Ranma catches what Happosai threw at him and sees that it was a hot ember. Before Ranma can do anything else, Happosai uses another ember which he places on Ranma's back. After Ranma jumps around in pain from the burning ember, he proceeds to send Happosai flying through the Dojo roof.

Looking on Soun and Genma comment on how little Happosai did and how unlike their evil master that is...

The Next Day
On their way to school, Ranma notes how his back still burns from yesterday when Kuno appears, charing towards Ranma. Ranma responds how he usually does by kicking Kuno in the face, however, Kuno soon recovers at hits Ranma on the head with his whilst asking Ranma if he calls that kick as he hardly felt anything. Unconvinced, Ranma kicks Kuno again and tells him to quit the tough act, but this just infuriates Kuno who demands Ranma fights him for real. Angered himself now, Ranma launches a flurry of punches at Kuno, but this doesn't stop Kuno from rendering Ranma unconscious with one blow.

Seeing that he has finally defeated Ranma Saotome, Kuno wastes no time in moving in on Akane and declaring her as all his, but this angers Akane who proceeds to send Kuno flying. Akane then returns her attention to Ranma and asks him what's wrong as well as how he could allow Kuno to defeat him. Frustrated, Ranma proceeds to punch a wall, but a small boy gets in the way. Ranma instantly panics and asks the boy if he's alright, to which the boy replies that of course he isn't. The boy then flicks Ranma's head, which causes it to bend backwards.

Concerned, Ranma and Akane go to Dr. Tofu's Clinic, where Dr. Tofu is terrified to find a mark on Ranma's back which indicates he's been subjected to a technique Dr. Tofu thought had died out centuries ago, the Ultimate Weakness Moxibustion!

Dr. Tofu explains that in ancient texts there's a reference to a technique with which anyone burned with this Moxibustion can be reduced to the weakness of a baby. Ranma quickly realises that this was what Happosai did to him last night, to which Akane asks if there's a cure. Dr. Tofu painfully reveals that there is no cure the Moxibustion as the counter technique no longer exists. Ranma is horrified with this news and runs out of the room in silence.

Catching Happosai
Meanwhile, Happosai is busy sending out letters to everyone across town, some of which are received by the likes of Kuno, the Principal and Mousse. When Ranma finds Happosai he greets the old lecher with a kick to the back of the head, which Happosai compares to a fly landing on his head. Infuriated, Ranma tries to grab Happosai, but he easily evades the attack and laughs before telling Ranma that his real revenge hasn't even started yet.

At the same time, Akane finds P-chan and notices he's gotten one of the letters Happosai was delivering earlier. Akane looks at the letter and is horrified to see that it reads "Ranma is Weak!". Happosai then tells Ranma that everyone who has a grudge against him will come lining up to get payback. Ranma retorts that by that time he'll have beaten Happosai to a pulp and made him change him back. However, Happosai easily overpowers Ranma. As Happosai celebrates his easy victory, Ranma warns Happosai he'll let him go... this time as Akane looks on and notes that at least Ranma's attitude hasn't changed...

Cast in Order of Appearance

 * Ranma Saotome (male)
 * Happosai
 * Genma Saotome (panda)
 * Nabiki Tendo
 * Akane Tendo
 * Kasumi Tendo
 * Soun Tendo
 * Genma Saotome (human)
 * Tatewaki Kuno
 * Tofu Ono
 * Principal Kuno
 * Mousse (duck)
 * Ryoga Hibiki (P-chan)

Trivia

 * The kanji that is left on Ranma's back from the moxibustion (貧) is "poor", whilst the character 灸 that is on Dr. Tofu's book is "moxibustion".
 * In the Viz Media translation, the cards Happosai distributes telling everyone that Ranma is weak have "Happy Gram" written on them. In the original Japanese version, they simply include the first character of his name inside a circle.