Lightwardens (大罪喰い, Ō Tsumikui?, lit. Great Sin Eaters), also known as Wardens, are powerful creatures of primordial Light in Final Fantasy XIV. Introduced in Final Fantasy XIV: Shadowbringers, Lightwardens take command of the sin eaters in a surrounding region. Though the sin eaters are motivated by only the basest of instincts, such as hunger, even they answer to a hierarchy, and follow the most powerful among, thus giving rise to what the locals of the First dubbed Lightwardens.
Emerging in the First after the Flood of Light was briefly halted, the Lightwardens began taking foothold in Norvrandt, the last land in the First not consumed by the Flood, and began to plague the survivors. Since a Lightwarden's aether could corrupt those who slay them, allowing them to reconstitute themselves, it proved near impossible to destroy them. Despite this, the Crystal Exarch discerned a weakness in the Lightwardens and found a solution in the Blessing of Light. With Hydaelyn's blessing, the Light of a slain Lightwarden could be contained, allowing night and darkness to return to the afflicted region. Just as an insect colony would perish in the absence of its queen, the sin eaters would scatter in droves.
Strangely, Lightwardens of more unique nature, such as Titania and Innocence, are capable of emitting a disorienting screech or roar that can almost knock out ordinary beings. This may be due to their hybrid nature rather than being full-fledge Lightwarden, as both Titania and Innocence were capable of not only of speech but also of strategic thought. Innocence, especially, was able to gather an army of sin eaters, command them to attack his foes and change parts of Mt. Gulg into a palace-like abode.
Ultimately, with the Warrior of Light's blessing, the Lightwarderns' essence was able to be contained, allowing night to return and sending the sin eaters to retreat. However, the amount of Light aether proved too much for the Warrior to contain alone, threatening to turn them into a powerful Lightwardern themselves, one powerful enough to bring about the end of the First. It was only Ardbert, the First's Warrior of Light, sacrificing himself by merging his soul with his Source counterpart, that such a fate did not come to pass, stabilizing the Warrior's soul.