Isshiki
A thousand years ago, Isshiki came alongside Kaguya to plant a tree and harvest its chakra fruit.  Kaguya was planned to be sacrificed to create the chakra fruit. Kaguya betrayed Isshiki and left him on the verge of death and destroying his lower half. There was a monk nearby, named Jigen. Isshiki didn't have enough chakra to use sukunahikona on him, so he shrunk himself and went into the monk's ear. Then he absorbed all the nutrients and then infused the karma seal on him.