Sealed polar particles.
Polar particles (極粒子, Kyoku Ryūshi, English TV: Ultra particles) are a mysterious substance mentioned in one of the legends surrounding the Sage of Six Paths. Because of his time as a jinchūriki, the Sage developed a disease that caused his chakra pathway system to start deteriorating, threatening his ability to continue using chakra. The Sage travelled to the Land of Redaku and began charting the heavens in search of a cure. He eventually met Janmāru-Tataru, founder of the Astronomy Research Institute.
One night, while the Sage was under Tataru's care, a meteorite passed through the sky; the Sage caught this meteorite and carefully cut it in two with only his chakra. One of these halves immediately dissolved into dust, dubbed by Tataru as "polar particles". The dust enveloped the Sage and healed his body. The Sage hid some of the leftover polar particles in a lake near the Institute, leaving instructions about how to retrieve them in the guise of a game called Hoshinarabe. A thousand years later, Sakura and Sasuke Uchiha were able to acquire these polar particles in order to give them to Naruto Uzumaki, a jinchūriki suffering the same disease as the Sage. Jiji also sought the polar particles for some unknown reason.