Although the tale of Princess Kaguya is well known, there is one common aspect typically forgotten in the story by some who tell it: as the princess returned to her home on the Moon, she gave an offer to the bamboo cutter who originally found her a Potion of Immortality (不死の薬,Fushi no Kusuri) to allow him to live forever due to his kindness; however, the bamboo cutter burned the potion not wanting to live a longer life without her and spread the ashes of it's remains on Mt. Fuji. Though the ashes remained behind, the means to finding the potion became a means of unlocking it on Mt. Fuji by finding the five "treasures" (the Dragon Neck Ball, Buddhist Stone Bowl, Hourai Ball Branches, a Firerat Fur Coat, and Swallow's Cowrie Shell) that Kaguya had forced wooing suitors to find in order to win her love.
The Boukengers end up becoming involved when the mysterious "Phantom Thief Selene" challenged them to find the five treasures, made even more difficult due to her own search for them and Ryuuwon's own interest in the Dragon Neck Ball. With the assistance of Souta, Selene is able to gain all five and thus the potion; but its ash unexpectedly gives a power-up to Wicked DragonLindom, who follows along after finding out about her true intentions, and ends up growing as a result. After the Boukengers defeat Lindom, Selene reveals that she was truly Princess Kaguya and that she led them on the chase in order for them to gain this Precious for themselves; likewise, the potion didn't truly give immortality as in the tale but actually merely gave a temporary power-up to those who partook it. She then used her powers to change the ash into a stone, which she entrusted to the Boukengers.