Byakugo is known as the yin seal and it absorbs the users chakra. Karma may be a more powerful version of the same jutsu. I believe that its related to six paths chakra. Because karma is directly related to the six paths of rebirth and the rinne cycle. In fact karma is the force that determines one's path. So its at least remotely related to six paths chakra and the Shinju. My guess is that it is one of secrets that the uzumaki had been hiding that got them destroyed. I say they are yin and yang because karma seals allows one to absorb and use chakra from other sources while byakugo allows one to store and use chakra from within. While ya playin byakugo probably has a six path version.