He was formerly one of the Four Devas of the Acacia Dragoons. While investigating the Divine Dragon Falls, he was killed by a madden Radius who was affected by Masamune's evil energies. His memories remained strongly connected to El Nido and they manifested into a "demon" who protects Einlanzer from unworthy wielders. His apparition also appears when Karsh and Dario encounter Masamune for the first time. In the Home World, his spirit also appears when Dario is possessed by the sword once more.
Serge and his party need to face Garai on the Isle of the Damned near the end of Disc One, as defeating him is necessary in order to obtain the Einlanzer. It has the power to break the curse caused by Masamune blocking Death's Door. Garai has an innate element of white.