Sylphiel's homeland is Sairaag, a port city located in the Empire of Lyzeille off the coast of the Demon Sea. Sairaag is famous for Flagoon, the gigantic tree in the center of the city, which their spirituality is based on and for being a center of practice for white magic. Not much is known about the way of life in Sairaag aside from what is seen in Sylphiel's memories and flashbacks.
Like all other cities, Sairaag has had its share of crime and terrorism, however a wall nearly twenty yards tall borders it to keep unauthorized intruders from entering the city. The town itself is made up of two sections. One is referred to as just Sairaag and the population is far larger than what would be expected of a city its size. Then there is Old Sairaag, which is adjacent to Sairaag and had been destroyed by a mazoku, named Zanaffar years ago.
Over a century ago, Gourry's ancestor the Swordsman of Light fought against Zanaffar who had been terrorizing the city. Zanaffar was destroyed by the Swordsman of Light and in order to protect the people, he contained the evil miasma Zanaffar's dead body gave off by planting a seedling, which would soon grow to become the holy tree Flagoon.
Flagoon had become a symbol of hope and reassurance for the people of Sairaag and they looked to it to give them guidance. Sylphiel especially had a special kinship with the holy tree from spending much of her time playing there. When Sylphiel was a young girl, Sairaag was again attacked by a rampaging demon that was stopped once more by a swordsman who carried the Sword of Light. It was Gourry who had eventually inherited the sword down the line of his ancestors.
In Episode 19 of The Slayers, Kopii Rezo destroyed half of the city using a very powerful black magic spell. It left the majority of the city in ruins and many of the people dead, including Sylphiel's father Eruk. Though Sairaag was built around Flagoon it is revealed Old Sairaag -- the ruins of the previous foundation of the city -- was located farther away from the tree from the time when Zanaffar first attacked.
With his strong desire to become better than the real Rezo, Kopii Rezo used the transcript of the Claire Bible so that Zanaffar would be reborn. Kopii Rezo absorbed Zanaffar's energy and he used his newfound power to provoke Lina into battle, destroying much of what was left of Sairaag. After helping Lina recover from a fatal wound in the ruins of her home, Sylphiel went to a lake inside Flagoon's secret rooms under its roots where there hung the holy sword of Sairaag, the Bless Blade.
The Bless Blade is the core of Flagoon's power and is able to resonate with Flagoon and can convey the will of the person who holds it. Lina took the Bless Blade and impaled Kopii Rezo onto Flagoon with it. Sylphiel then used the healing spell Recovery on the holy tree Flagoon and, in combination with the Bless Blade, it absorbed all the miasma thus killing both Zanaffar and Kopii Rezo.
At the end of Slayers, reconstruction of Sairaag had begun but by the time Sylphiel appeared in Slayers NEXT, it looked as though the attempt had been abandoned. She went along with Lina and co. after hearing a rumor that Flagoon had died and a new city had been rebuilt. Upon going to the city, Sylphiel realized that this was not a new city but an exact replica of Sairaag before it had been destroyed. It is then Sylphiel is reunited with her father Eruk who had died in The Slayers.
According to Eruk, Hellmaster Phibrizzo had regenerated the entire city as well as the dead, making them his slaves. So Lina set off to Hellmaster's temple that is located where Flagoon used to stand. Phibrizzo used the dead against the Slayers by having the zombies attack them until he decided to bring them all into his temple to kill them off one by one to provoke Lina into using the Giga Slave so that the world would be destroyed.
Lina does indeed cast the Giga Slave but it does not go the way Hellmaster planned and instead of the world being destroyed, he himself is destroyed by L-sama who was invoked into Lina's body. With Phibrizzo gone, the false city collapsed on itself and the dead go back to the world of the afterlife. Sairaag is still in ruins however, but it is Sylphiel's wish to one day reconstruct her beloved home.