The Seru-kai (獣 [セル] 界, seru kai, lit. Seru Realm) is a location in Legend of Legaia. It is the birth place of all Seru, Ra-Seru, and Genesis Trees. Vahn, Noa, and Gala visit it twice - once in Rogue's Tower and once in Noaru Valley.
In the beginning there was Tieg, the god of Legaia. Tieg divided himself into two: human and Seru. He also divided the world into two: Legaia and the Seru-kai. To govern Seru-kai, Tieg chose a small group of Seru and gave them special powers. These were the Ra-Seru.
A Mother Genesis Tree was created in the Seru-kai which held all the power of the Seru-kai, as well as the power of the Seru and the Ra-Seru. When Tieg divided his body into human and Seru, the Seru were entrusted with order. Tieg had faith in human potential, and ordered the Seru not to interfere in human affairs.
The Seru-kai and Legaia were destined to remain apart, however a group of Ra-Seru plotted a rebellion against Tieg and allowed the Seru to enter the human world. Tieg stopped the rebellion with his strength and banished the rebel Ra-Seru, but humankind had already learned of the Seru's power and built civilization.
After the Rogues rebelled against Tieg the mighty god put down the rebellion with his power and banished them from Noaru Valley. Rogue's Tower became the domain of the Ra-Seru who plotted against Tieg. The tower is itself the body of the head Rogue who lead the rebellion against Tieg and multiple other Rogues reside in it.
Rogue's Tower is filled with gloomy stone walls that hold eternally-burning wax candles. Many of the rooms lead in dead ends and the only way to travel through the tower is by stepping on strange glyphs that are spread out all over the tower. Every few seconds the tower will warp, causing the candles to turn into purple balls of fire and the walls and floors to become covered in pulsating veins.
While the tower is in this state every single glyph on the floor will lead to a trap room that leads nowhere. Because Rogue's Tower is located in the Seru-kai, multiple Seru can be found. Some are only found while the tower is in its normal state while some are only found while the tower is covered in veins.
The Rogues appear in the form of levitating crystals and look very similar to Ra-Seru. The main difference between Ra-Seru and Rogues is that the Rogues are sinister and evil in nature whereas the Ra-Seru fight for good. The head Rogue that embodies Rogue's Tower breathes a substance that causes normal Seru to go mad with its presence - the Mist.
However, the Mist that flows over Legaia does not directly come from Rogue's Tower. The first Mist Generator that was built received its Mist from Rogue's Tower, but after the gateway was sealed the henchmen of the Mist discovered how to create the same substance by using Ra-Seru and Ra-Seru eggs. By combining a Ra-Seru or Ra-Seru egg with a Mist Generator they were able to replicate the same Mist from Rogue's Tower and spill it over the planet.
Noaru Valley is the original home of all Seru, Ra-Seru and the Great Genesis Tree. It is also where the god Tieg resides. The power of Noaru Valley is sustained by the Great Genesis Tree.
Noaru Valley consists of see-through crystalized walkways and surrounded on all sides by a bright, cloudy sky. Yet the death of the Great Genesis Tree causes the sky to go dark and thunder and lightning to fill the area. As it is the Seru homeworld, multiple Seru can be found in Noaru Valley.
Access to Noaru Valley can only be gained by most through summoning Tieg in Uru Mais. However, one has demonstrated the power to teleport to Noaru Valley with its own abilities.
The Ra-Seru heroes first travel to the Seru-kai in Conkram of the Past in order to shut off the Mist flowing into Conkram, which was coming from the Seru-kai itself. The Ra-Seru tell Vahn, Noa and Gala that they are going to Rogue's Tower, which is located within the dimension of the Seru but also the body itself of a Rogue Ra-Seru. After battling multiple Rogues they reach the head Rogue and destroy it, cutting off the source of the Mist and removing the gateway to the Seru-kai.
Unfortunately, after the Mist incident two Rogues from Rogue's Tower escaped into the human world. One of these Rogues fused with the town of Conkram and turned it into a living, breathing Sim-Seru fed by Mist from the Absolute Fortress. The other Rogue was said to have awakened Prince Cort's evil ambitions.
The Ra-Seru heroes soon find themselves having to return to the Seru-kai. This time, however, they must travel to Noaru Valley, the place Legaians believe souls go to after death. Vahn, Noa and Gala must travel to Noaru Valley in order to save the Seru-kai from being conquered at Songi's hands - for if they do not, all Seru and Ra-Seru within Legaia and the Seru-kai will die.
Meta, Terra and Ozma tell their wearers that they can only reach Noaru Valley by way of Uru Mais. After traveling to the destroyed ruins they discover that the whispers are still present even though the pyramid had been blown up by Juggernaut. With their prayers they summon Tieg, who opens a portal to the dimension of the Seru-kai and drags the Ra-Seru heroes in with his power.
The heroes find a heavenly place filled with crystalized floors and clear sky. Reaching the Great Genesis Tree, they find Songi sapping the energy from it with his Sim-Seru. With Songi empowered further and the Ra-Seru starting to weaken due to the Great Genesis Tree's loss of power, the battle between them is the toughest yet.
Miraculously, the Ra-Seru heroes prevail and defeat Songi. After the death of his hybrid Ra-Seru/Sim-Seru Jedo, Songi starts to turn gray and writhe in pain before exploding into bits. It is then that they learn that the Seru-kai is intolerant of the presence of normal humans, therefore any human not wearing a Seru will be vaporized moments after entering the Seru-kai.
Though Songi is defeated, it appears that the Seru-kai is going to die moments after. The heroes fear that they will die with the Seru-kai, but soon the familar figure of Hari appears underneath the Great Genesis Tree's branches and temporarily restores its life. However, they reveal that they cannot keep it from dying and that it is the will of Tieg for the Seru-kai to die.
The Ra-Seru use their powers to warp to Mt. Rikuroa's Genesis Tree and proceed to return to Rim Elm where they face Juggernaut. Soon after the destruction of Juggernaut, Meta, Terra and Ozma reveal that the Seru-kai is just about ready to die and use the last of their powers to disintegrate the Bio Castle and return everybody in Rim Elm to normal, as well as restore everyone to perfect health - even going so far as to reincarnate Cort as a baby and give him a second chance at life. With the destruction of the Seru-kai, all Seru on Legaia begin to lose their power and eventually die out.
- Because the Memory Statues received their power from the Seru-kai they all stop working after its destruction and therefore it is impossible to save the game after the Bio Castle is destroyed