It is called Gudoudama or Truth-seeking ball which was gained by Obito after being Ten Tailed Jinchuriki.
Truth-Seeking Balls are hand-sized orbs of black chakra that users can use to alter its shape to serve for a variety of purposes.
When one awakens Six Paths Senjutsu, Truth-Seeking Balls appear and float behind their back. This can be done by becoming the jinchūriki of the Ten-Tails or by entering Six Paths Sage Mode.
And stated in its usage
Truth-Seeking Balls are composed of all five basic natures, in a way similar to yet surpassing kekkei genkai and kekkei touta. If imbued with Yin–Yang Release, they can be used to neutralise ninjutsu and by extension become impervious to it; this negates the regenerative qualities of the Impure World Reincarnation, making it possible to kill or permanently damage those who have been reincarnated.