Stamina comes with all Soul Workers. This resource is what allows Soul Workers to evade (ground and air) as well as use the Special Dodge, Rising Attack, and Rising Roll skills. The resulting invincibility frame (often abbreviated as "iframe") allows the Soul Worker to avoid damage; the iframe also allows passing through monsters like mist, making it invaluable for rapid reposition.
It shows up as a mid-screen bar when used. It remains visible until full and unused for several seconds, at which point it fades. Total stamina can also be viewed in the Soul Worker's profile (default key: p).
Stamina is self-sustaining, but recharges slowly. Players can improve its recharge by investing skill points (SP) in Stamina Mastery (+10% recharge speed per level), though it's more advisable to stop at levels 3 or 4 given the SP cost goes up. Given the rarity of in-game consumables for restoring stamina, recommendation is use Akashic Records until get Cell and/or Megiddon (latter being more recommended); Cell has a chance to give stamina per hit and Megiddon restores a percentage of stamina every 5.5 seconds.
Additionally, stamina has a base value of 100. Certain weapon familiar, armor drives, equipment stats, and gear set bonuses raise this maximum while equipped; endgame geared players with 150+ stamina are fairly common. Stamina recharge rate uses total stamina, so both Cell and Megiddon ARs restore more stamina if the player has a higher stamina value.
Numerically, evasion on ground uses 15 stamina. In the air, it uses 40 stamina. Airborne soul workers can chain basic airborne attacks between evading.
Note that attacks that suck in Soul Workers, such as Yorhaka's inhale-bite in Altar of Void, overpower any airborne evasion. In those situations, airborne evading is potentially deadly to the player. Also, be aware certain special moves like Yorhaka's bomb and Rafakumba's "God of wickedness" cannot be dodged with iframes.