Prayer Reverie is only seen in the manga series Gundam SEED X Astray .
He was the former pilot of the experimental ZAFT DRAGOON suit YMF-X000A Dreadnought that was used by the Junk Guild before he died due to genetic complications. He was a little child that had extremely good Newtype potential. Apparently, he used to pilot a prototype TS-MA2mod.00 Moebius Zero gunbarrel equipped mobile armor before he stole the Dreadnought Gundam. Even after the war, Prayer's origins are still unknown; however, there is some speculation that he is a failed Al Da Flaga clone. This could be true because according to Rau Le Creuset, before he was cloned, there were several unsuccessful attempts and Prayer could be one of these "faulty" clones.
He used to fight constantly with Earth Alliance mobile suit pilot Canard Pars and his CAT1-X1/3 Hyperion Gundam Unit 1, who himself is considered a failure because Canard is the only failed "Ultimate Coordinator" "prototype" to survive. In the final battle, the Hyperion Unit 1 is destroyed, but Prayer protects Canard from the explosion of Hyperion's nuclear reactor. Unfortunately, Prayer later dies from unknown causes. This here is another part of the speculation: Rau Le Creuset suffered from pains from his own imperfection, and so did Prayer.