Oni Regeneration

The incredible fortitude and longevity of your ancestors flows through you, granting you the following benefits:

• Increase your Constitution score by 1, to a maximum of 20.

• As a reaction when you take damage, you can spend a number of your Hit Dice up to your proficiency bonus to heal yourself. Roll the dice, add your Constitution modifier, and regain a number of hit points equal to the total (minimum of 1). You can use this benefit a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.