Rainer Milan (ライナ・ミラン Raina Miran ) was Adlet Mayer's best friend.
Rainer and Adlet were best friends. Since they were the only boys in their village, they decided to become their village's defense force, even though Adlet wasn't interested. He was killed while helping Adlet escape death from the villagers. However, it is revealed that he survived thanks to Tgurneu healing him where he worked as a slave under his control.
He escapes after obtaining a map from the guards to the mountains where he meets Nia Grasta, who confesses to the truth of the Temple of the Goddess of Fate and bestows him the ability to avoid the fate of death albeit in a weaker form as it grows weaker when passed down from person to person.
Rainer later becomes a Corpse Soldier and is unable to move his body, as he is under the control of one of Tgurneu's Dark Specialist. The power passed by the acolyte help him to maintain his sanity and mind, and for a short period of time he could move his left hand momentarily and so he carved into his skin that he was alive.
Later in the battle with the Braves of the Six Flowers, Rainer constantly attempted to make contact with the Braves only to fail as they were determined to break through the Corpse soldiers instead of saving them. Eventually he loses his right arm which was the last proof he was alive and was soon incapacitated by Chamo;s Jyuma. Eventually Fremy killed Dark Specialist 9 whose power was the reason the corpse soldiers were alive in the first place which caused Rainer to slowly die in pain. Before he died he was able to use his throat to sing a song to indicate where he was. It was thanks to this that Adlet found him before he died and he reveals to him, Hans, and Rolonia of the Black Barren Flower. He tells them that the Black Barren Flower is a Sacred Instrument capable of absorbing the powers of the Crests of Six Flowers the closer they get to the center of the Wailing Demon Territory. He reveals that the Black Barren Flower has the form of a human girl with white hair, a single horn, and cold eyes. He dies as he takes one last look in Adlet's face saying he reminds him of his friend and passes with the feeling of accomplishment for being a hero who helped the Braves.