Alfonso San Valiante is the crown prince of the kingdom of Valiante. On his twentieth birthday, his mother, Queen Esmeralda, gives him a golden pendant she had owned throughout her life. Embedded in the pendant is the symbol of Garo, a red gem in the shape of a triangle contained within a golden circle. Alfonso is noted to have been a fairly frail and sickly child, however, he managed to grow up as a strong, healthy, and formidable swordsman. Despite his status as a prince, he holds a down-to-earth attitude and treats all people kindly. Alfonso is also courageous and intensely committed to his royal duties, willing to go to any length to protect his kingdom and people. When his father's adviser Mendoza usurps the crown, Alfonso managed to escape capture, going about as a fugitive to seek out the Knight of Light to correct the wrongs. In his travels, he finds a mentor in Rafael Banderas, also known as Gaia the Knight of Defense, who agrees to teach him the ways of the Makai Knights.

(Source: MAL)

The story of the anime begins when the king's adviser launches a witch hunt, which endangers the Makai Knights and Makai Priests, who are supposed to protect people. A Makai Priest who has been condemned to die at the stake gives birth to a child, Leon Lewis. The child is rescued by his father, a Makai Knight, but never meets his mother. When he grows up he inherits the Gold Armor as a descendant of the Gold Knights. Meanwhile the king's adviser has taken over the country as the king has become ill, and Prince Alfonso has been driven out with his mother. He comes seeking the legendary Gold Knight in hopes of retaking his kingdom.
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(Source: Anime News Network)

A sequel set 4 years after the TV anime "Garo: Honoo no Kokuin."