Sylphiel is a priestess of the shrine to Flare Dragon Ceifeed in Sairaag. When she was young, she took the Bless Blade from the shrine and hid it under the holy tree, Flagoon. This later proved to be useful, as the sword was needed to defeat Copy Rezo-Zanaffar. After each destruction of Sairaag, Sylphiel was involved in the efforts to rebuild it. Her life revolves around helping other people.
Sylphiel is an extremely gifted cleric of white magic. She's more powerful in the art than other white magic-using characters like Amelia Wil Tesla Saillune and Naga the Serpent. Unfortunately, her skills in other areas of magic are lacking. She has not mastered the basic fundamentals of offensive magic like shamanistic or black magic spells. The most famous example is her version of Flare Arrow, which looks more like a small carrot than an actual Flare Arrow.
Sylphiel is openly attracted to Gourry, and this makes Lina uncomfortable.
(Source: kanzaka.wikia)