Reeah arrived in Hira centuries ago. Back then it was a tiny serpent that could have easily been killed, but it was found by the Shadow Lord's servants, who were posing as rat catchers in order to breed a rat plague through the city. They fed their rats to Reeah, thus allowing it to grow larger.
The Opal dragons sensed an evil presence within the city, possibly referring to Reeah or the grey tide.Hopian told Doran that he intended to destroy the evil when the city was inevitably abandoned, but the dragon was convinced into hiding before he could do so.
The rat population in Hira eventually grew out of control, forcing the people of Hira to abandon to their city and found Noradz under the leadership of the rat catchers. With the city abandoned, Reeah claimed Hira for itself.
The Forests of Silence
After the Shadow Lord's invasion of Deltora, it chose the City of the Rats as the hiding place for the great Opal. An Ak-Baba delivered the stone to the city, and Reeah had it set onto a golden crown that it wore. This allowed Reeah to access the Opal's power to see the future.
City of the Rats
When Lief, Barda, and Jasmine arrived in the City of the Rats to search for the Opal, Reeah used telepathy to compel Lief towards the meeting hall, where it was waiting. It attempted to get Lief to discard the Belt of Deltora, but Lief touched the Topaz, which frees his mind from the snake's influence. Thanks to the power of the Ruby, Reeah was momentarily held back as well, though it told Lief that his magic would not protect him forever.
To allow Barda and Jasmine time to surround Reeah, Lief distracted it with questions and idle praise about its past. Reeah happily obliged and revealed its history, as well as the truth behind the rat plague. Lief also told it that the people of Hira later founded the city of Noradz, but Reeah did not care.
Growing bored with talk, Reeah attacked Lief and knocked away his sword before using its tail to incapacitate Barda. Lief, in desperation, threw his jar of Fire-Beads at Reeah's mouth, but missed and set fire to the weakened building. Reeah snatched Lief in its jaws and raised him high in the air, taunting the boy before preparing to swallow him whole. However, this allowed Jasmine to approach on the rafters with Lief's sword and slice Reeah's throat open—though she had to use nectar from the Lilies of Life to revive Lief from the fall. Reeah's dead body was then devoured by the hoards of rats.
While fleeing from Kirsten, the Guardian of the Sister of the North, Lief fell into a pit of snakes. The Sister was hidden among them, and its despairing cry caused Lief to remember Reeah's voice and nearly discard the Belt of Deltora. However, he remembered that the Ruby repelled Reeah, and by extension, the other snakes in the pit, which allowed him to regain his senses.
Reeah was an enormous snake with a body as wide as an ancient tree trunk and flat, cold eyes. Its size was so great that it could fill the entire floor space of Hira's meeting hall while coiled. It had green, shining scales. Reeah wore a golden crown on its head with the Opal set in the crown's centre. When Reeah first came to Hira, it was the size of a worm and could have easily have been stomped to death, but eventually grew to a monstrous size, able to swallow a man whole.
In the anime, Reeah had three heads and considerably darker scales. It also looked more like a hydra as opposed to a snake, with six mandibles making up its mouths, and spines growing from its underbelly. The crown on its head is also much smaller and resembles a tiara. It rests on the spike on the middle of its head.
Reeah was an extremely vain and proud creature. It repeatedly referred to itself as "all powerful" and "the One". It considered itself to be the greatest of the Shadow Lord's servants and looked down on humans. Reeah was easily flattered and did not shy from the opportunity to boast about its own magnificence. The Shadow Lord was the only being that Reeah seemed to have any respect for and acknowledged that the Shadow Lord gave it its "kingdom".
Reeah's immense size gave it equally immense strength, able to knock Barda unconscious with one swing of its tail. Despite its size, Reeah was also very quick and its fangs were poisonous. It claimed that it could put out the roaring fire that Lief started with a single gust of breath. While in possession of the Opal, Reeah was able to see briefly into the future. It was able to read and control Lief's mind to a degree, though its mind control could be counteracted by the Topaz. It could also speak to Lief telepathically, though it never displayed these abilities on any other character. Reeah was apparently repelled slightly by the Ruby.
Reeah's role in the anime is the same as the books, but with several noticeable differences. It is depicted as a hydra with three heads, though the other two weren't revealed until after it had been stabbed by Lief, which caused its body to flash with orange light, so it is possible it only grew new heads once it took damage. It also told Lief that the rats that invaded Hira were its servants; they invaded the city on its orders rather than being bred by the Ra-Kacharz like in the books. Apparently this was done to protect the Opal, which brings up continuity issues regarding when the people of Hira founded Noradz.
The battle with Reeah is much different than in the books, with both Barda and Jasmine actively participating. Shortly after growing its two extra heads, Reeah swallow Lief, but spat him back when Jasmine attacked with her knife. Barda caught Lief to break his fall and then engaged Reeah himself before being tossed aside. This allowed Lief to get back up and strike the crown off of Reeah's head. Once the crown was removed, Reeah's heads began to thrash wildly, knocking Lief into a pillar that nearly kills him and destroys a large section of the city, rather than Lief falling from its mouth and the Fire-Beads destroying the city as in the book. Why Reeah did this and what happened to it are unknown, as it is never seen again in the series.
Reeah was the only gem guardian that actually used the power of its gem, using the Opal to determine Lief's name.
Of all of the dangers that Lief faced, Reeah came the closest to killing the young king, albeit inadvertently, due to its immense height. Lief was only saved by the nectar from the Lilies of Life.
Reeah is never called by gendered pronouns; in the books it is always referred to as "it." An edition of City of the Rats that came with trading cards had a short bio describing Reeah as "she", but this was not reflected in the text.
In the anime, Reeah seems to survive, though it is never seen again.