The Stamina bar
Tonight we go into a bit more depth about the stamina bar mechanic.
Sen's weapons and artifacts are tied into this gauge. As long as sen's gauge has energy in it, She can fire her pistol. Each shot takes away a small amount of energy, so if you shoot too much your pistol will overheat/run out of energy. The charge shot will take out several normal shot units to power the pistol.
Stamina will recharge over time so as you're using your pistol, your stamina replenishes slowly. You will be able to pick up power ups to replenish your stamina quickly as well.
As for artifact themselves they use more energy than your pistol and your charged shot. Each artifact weapon's use will use different amounts of stamina, and if say the shield artifact is being used it will steadily drain the gauge.