Amulet of Fokasu

An amulet worn by the Shiroi Monastery senseis, it is a silver amulet marked with the symbol of the monastery on a silver chain 

This amulet can store the ki of the wearer, as a bonus action you can store any number of ki points you currently have in the amulet, and you can withdraw any number of ki from the amulet as a bonus action. The ki remains as it is until you take a short or long rest, after the rest the amount of ki in the amulet is divided by 4 (i.e. if you put 8 ki points into the amulet then take a short rest there are 2 ki points in the amulet).