The Guardian is a being as old as the world's cycle (around 10 million years), whose appearance changes depending on the beings observing her.  She stays at the Bottomless Land waiting for the person who has the key to open the passage to the bridge to the Realm of Mind. 
|It is later discovered that she is actually part of the Custodian's thoughts fused into a self-cognitive being which was formed after it began experiencing divergences. With a sufficently long time she was born within the Custodian, but not only her, Lan and the other Apostles were born under similar circumstances.|
Even though they just met, Joan believed that the Guardian was a nice person and that it would not lie to her.  Roland, on the other hand, seems to think her behaviour to be a troublesome issue, since the Guardian isn't expressing any hostility and might have a completely different concept on good and evil from human, then they might be treated like humans treat birds: no one treated birds as enemies, but sometimes helped some injured ones or saved some from cats and other times killed a group of them if they stole grains.  Hackzord also seem to find her rather amiable, though lacking the imposing grandeur of a demon of high standing. 
She first appeared to Joan as she arrived unintentionaly at the Bottomless Land and helped her to heal her wounds. At that time she presented itself as a very pretty woman with two strands of black hair cascading to her chest and who was wearing a white dress. She eventually treated Joan's wounds with a medicinal cream and wrapped them with her dress. 
Later a POV part-chapter of her is released, which shows that she wished to meet with Joan again. By that time, she also believed that it was too late, since the last tranquility the sea would have till its end was happening at that moment. According to her this Battle of Divine Will might be the last one of the cycle. 
Afterwards, she meets Hackzord appearing as a female higher ascendant demon, with distinguished fingers and hair, dressed in light and white cotton robes. She eventually leads him to the bottomless pit due to his request to see the bridge to the Realm of Mind,  and eventually disappears after being attacked by him.
During Graycastle's attack against the Deep Sea Demons in the Bottomless Land, she eventually appears to Anna as a girl dressed in pure white and advises her to leave while there's still time. It appears that she knows about the Oracles and reveals that the Battle of Divine Will is an attempt to seek the answer. Right before disappearing, she tells Anna that if Roland really possess as much strength as Anna claims he does, then he would not need the bridge (Bottomless Land) nor the key (Complete Legacy Shard).
- Due to her understanding Joan, and Hackzord she might: have a way to communicate mentally, have a translator type magic or be very well versed in all types of languages. When tallking to the Guardian, Anna's voice didn't seem to come out from her throat, which might support the mental communication theory.
- As noted by Hackzord and Anna being attacked whithout realizing anything around them while talking to her, her apparison to them might be on the Realm of Mind.
- Chapter 1366
- Chapter 1401
- Chapter 1295
- Chapter 1490
- Chapter 1372
- Chapter 1294
- Chapter 1402
- Chapter 1483-1484