The Legendary Phoenix egg is an extremely rare egg from which a Legendary Phoenix can hatch. It is considered a magic charm which enables whoever owns it to master the Phoenix Sword (Sword of the Phoenix in the anime). Tatewaki Kuno came across an egg at the Antique Shop Yamatai and acquired it to master the Phoenix Sword.
In both versions the egg is quite large for a bird’s egg and has the character for "Shining Light" on its side. It has a mottled pattern around its lower side and comes in a nest of twigs, which is hatched with the egg itself. The egg can keep for an indefinite period of time and will not spoil. It will only hatch when it is placed on top of someone’s head and the phoenix that emerges will always be a female. It will only lay another egg when it leaves the nest.
The shop owner told Kuno that the egg was similar to a swordsman’s protective charm and that whoever possessed both the phoenix and its nest could master the Phoenix Sword. Going on the man’s word, Kuno offered to buy it but the owner held out, claiming that the Phoenix Sword was too heavy a burdern for a normal person to bear. When Kuno slapped him with a wad of yen he quickly changed his mind, but warned Kuno to never put the egg on his head.
While Kuno was contemplating the egg the street, a fleeing Happosai bowled him over and the egg was thrown into the air. Ranma Saotome, who was chasing the old man, caught it and was attacked by Kuno who was trying to recover the egg. He kicked Kuno in the face and, after Kuno demanded that Ranma return the egg, put the egg on top of Kuno's head. Just as Kuno started to explain why not to do this, the egg hatched with a blinding light and the phoenix was revealed. After Ranma succeeded in feeding the phoenix enough growth pills, it flew off after having laid another egg in a blinding light. The shop owner picked up the egg and vowed to seal it away before Kuno slapped him with a wad of yen and bought the second egg.
Kuno and Sasuke Sarugakure learn that the egg is a magic charm for martial artists and that whoever owns it can master the Ho’oken or Sword of the Phoenix. Kuno offers to buy the egg, but the owner tells him that no ordinary man can use the Ho’oken and that he will never sell it. However when Kuno slaps him with a wad of yen he immediately changes his mind.
After he and Sasuke leave, Kuno is wondering what kind of attack the Sword of the Phoenix is. Sasuke however is worried about the shop owner’s warning to Kuno to never put the egg on his head. Despite the owner repeating the warning from on top of his head before being sent skyward, Kuno scoffs at the warning before a baseball hits him in the face and he drops the egg, getting floored. However Ranma appears and catches it before it hits the ground. Kuno peels the baseball off his face and seeing Ranma with the egg, attacks him with his bokken. Ranma counters with a kick to Kuno’s face and, in response to Kuno's demand that he return the egg, places the egg on Kuno's head. The shop owner, who has returned, is dumbfounded at this and runs off in terror, while Sasuke blubbers in fear and Kuno is frozen. He is snapped out of his shock when Ranma tries to ask Sasuke what happens. Before Kuno can scold Ranma for what he has done the egg hatches, with a blinding light emerging from the cracking shell and the phoenix is revealed.
At the end of the following day and thanks to Ranma, Akane Tendo, and Ryoga Hibiki’s efforts, the phoenix grows to its largest size and emits a blinding light before flying away. Ryoga then notices that the phoenix has left behind an egg, meaning it was female. The shop owner picks up the egg and plans to seal it away, but Kuno slaps him with a wad of yen again and he agrees to sell it.