Aether Soul-Link

You exchange a portion of your life force, channeling it into a spell on which you are concentrating. When you cast this spell, you spend a number of Hit Dice equal to the level of the spell you are concentrating on as though you had spent the Hit Dice during a short rest, but you regain no hit points by doing so. Instead, the spell you're concentrating on extends its duration based on its original duration:

• A spell with a duration measured in rounds extends by a number of rounds equal to your Charisma modifier.
• A spell with a duration measured in minutes extends its duration by a number of minutes equal to your Charisma modifier
• A spell with a duration measured in hours extends its duration by 1 hour.
• A spell with a duration measured in days extends its duration by 1 day.

Once a spell has had its duration extended in this way, it cannot benefit from another casting of Aether Soul-Link.