Chakra is the power to connect and we already witnessed it on a spiritual and cosmic level with space time warping and real time travel along with dimensional travel plus otherworldly supernatural summonings
If people can get their soul sealed away forever or eaten alive by ghosts, and the Sage can exist as a force ghost to empower people eons after death, then Brook is getting it too.
Brook would see his shadow turn into that Ryuma Corpse and leave his body and flee in terror