Ki Drainer (5e Feat)
From D&D Wiki
Prerequisites: The ability to use Ki
You have discovered a way to take the ki from your enemies to use it to your advantage. You gain the following benefit:
When you make a melee attack against a creature that is not an undead or construct, you can use your bonus action to make them make a Constitution save equal to 8+proficiency+your wisdom modifier. On a fail, you gain 1 ki point. You cannot go above your Ki maximum with this feature and you can only use this feature once per turn.