Soul Well is a magical container that can contain a living soul. Once the living soul enters the Soul Well it can never get out of the relic. Gameplay wise, the Soul Well unlocks the ability called Shadow Fury, which increases Lo Wang's effectiveness in combat. The ability has a bar that needs to be refilled every time after use by collecting miniature Soul Wells dropped by enemies.
Lo Wang is first contacted by Yakuza who hires him to get the Soul Well from the Temple of Longing. After defeating the Soul Wells guardian, Lo Wang retrieves the relic and returns it to Yakuza, where they give it to Smith Masamune.