Fighter/7th/Tunic

Stamina Vessel

At 7th level, you learn to exert your techniques and strikes to the point of injury. At the start of your turn, you can roll one of your Heart Containers and add your Constitution modifier to the roll. In doing so you regain stamina points equal to the result. The Heart Container you rolled is expended, and cannot be used during a short rest or for other features, but is still restored when you finish a long rest.

Once you use this feature, you must finish a short rest before you can use it again.