Amor was the Pisces Gold Saint of XXI Century. He was the younger brother of Medea, and he and she possessed an awful dark power, and this did the citizens try hurt them. But, Medea, ever protect Amor, and Amor wished to follow his sister, for observes she bring darkness where her pass, and because this, he helps her with yourpain to bring darkness for the world.
Amor, because he was a Medea ally, already knew all her scheme for manipulating Mars and his darkness element. So, Amor, became a fake Mars servant, or, presumably received the Pisces Cloth from Medea with no Mars consent (because she has this authority), and because this, any Martian knew the existence of a Pisces saint.
Amor, protected Medea from Mikene (loyalest Mars servant) attack, and easily kill him. Later, Amor going to protect the Pisces Temple when Kouga, Yuna, Souma, Haruto and Ryuho arrive there. The Pisces Saint revives the 4 Four Heavenly Kings of Mars, to kill Souma, Ryuho and Haruto (he spared Yuna's life, because she is a woman, and because this, he flirted with her) to induce Kouga to awaken Abuz Cosmo (darkness).
After the death of Mars, Medea stole his power and give to Amor, that gets more power than before. But, for the conclusion of Medea scheme, he gives Mars power to Kouga, and he don't be processedimmediately, doing Amor confused. Medea confirms the Amor's suspicion: Medea just used Amor, to transfer the darkness of Mars to Kouga (and she tell it to him, for he irritates Kouga and do him became Apsu). Amor gets angry and decides to kill everyone and kill Kouga before Abzu posses him, and domain the World. But, Kouga gets possessed by abuse and kill Amor.