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.
Thousands of years of conflict boil down to a single confrontation. Shadow Angels, beings of pure destruction that have haunted humanity for over twelve millennia, finally make their move against Earth. Standing against them is Deava, a military organization pilot corps armed with Aquarion, a colossal mecha that demands something extraordinary from its pilots: the synchronization of human souls themselves. Apollo carries a secret buried in his very existence. He is the reincarnation of Apollonius, an ancient warrior bound by fate to face Touma, a Shadow Angel whose power threatens to erase humanity from existence. The weight of resurrection and the burden of predestined conflict collide as Apollo and his team discover that piloting Aquarion isn't just about mechanical skill. It demands emotional connection, spiritual resonance, and a willingness to merge consciousness with others. This two-episode OVA strips away the larger narrative to focus on the raw clash between reincarnated enemies. Expect intense mecha action layered with supernatural elements and the strange intimacy of warriors forced to share their innermost selves to survive.