You can't watch this without knowing the show already exists, which means the OVA assumes you've lived through the full series, and it repays that loyalty by finally letting Apollo and Touma stop being enemies and start being what they always were. The mecha fusion system becomes a metaphor for acceptance instead of a weapon system; two halves of the same fallen soul learning to coexist instead of destroy. It's a love story disguised as a war story, told through robots that only work when the pilots stop fighting what they are.

In a far future, an organization called Deava battles the Shadow Angels, creatures that have endured for more than 12,000 years with one goal: wiping out humanity. Apollo appears to be an ordinary human, but he is actually the reincarnation of Apollonius, a fallen Angel. Long ago, Apollonius was a slaughtering Angel who fell for a human girl named Celine at first sight. He abandoned his wings to side with the humans and helped them build the mecha warriors that gave them a chance in their war against the Angels. The Angel Touma, enraged at losing him, took revenge by corrupting a human. Now Apollo must fight Touma alongside his comrades to keep the Earth from being destroyed. The two-episode OVA blends mecha action, science fiction, the supernatural and romance.