Imperial Pearl

A pearl upon which the plans for a secret weapon, the "BioPanzer" tank, was inscribed within at the dawn of the 20th century by a scientist wishing to protect it's secrets from those who could use it. Tracked down by Shizuka of the Wind in hopes of merging it's power with Tsukumogami Takumigami, it ends up in the hands of a boy which Sakura (as BoukenPink) gives to and which he refuses to give back due to not trusting the human form of the Boukengers. Retaken ultimately by Shizuka and implanted within the blueprint-interpretor of Takumigami, it was used to recreate BioPanzer which is stopped by Sakura and the Bouken Shovel. The pearl returns to the boy, who finally gives it to Sakura claiming she'll hold it for "a friend" (BoukenPink).

A short while later, the Imperial Pearl was tracked down by Yuji Toba, an international spy hired by another nation hoping to use the plans for the BioPanzer for their war machines. With the assistance of the Questers, he captured his former partner Souta to gain access to the SGS storehouse and the pearl, but Bouken Blue ultimately convinced him to move on just like he had from his spy life, stopping the plan and keeping the pearl safe.