The 21st century was supposed to mark the beginning of mankind's golden age of space travel. However, humanity's lingering dreams of the stars are shelved when Earth suddenly comes under attack by alien entities. Trampling across the planet's surface, these giant invaders leave nothing but death and destruction in their wake. Having suffered personal losses from the invasion, Takuto Kaneshiro joins the fight against the extraterrestrial enemies. In his quest for vengeance, the disillusioned young Takuto must seek out any possible allies, but the line between friend and foe is dangerously thin. When old powers crumble and new opportunities arise, many are prepared to capitalize on the chaos. Takuto soon realizes that the aliens may be the least complicated obstacle to uncovering the greater truth behind the catastrophic invasion.

The successor and branch manager of the Himeya Company—one of the many Undine associations housing female gondoliers—Aika S. Granzchesta surprises everyone when she rejects tradition and refuses to inherit the company's legendary gondola. Aika's apprentice Azusa B. McLaren, unable to wrap her mind around her mentor's unexpected decision, confronts her directly but to little effect. To better understand her reasoning, Azusa and her fellow Undines secretly plan to arrange a meeting with Aika. With the much-awaited winter days in sight, accompanied by the tranquility and sublimity of Neo-Venezia, Aika reminisces about her journey as an Undine that forged her into the person she is today. As she vividly remembers all those invaluable experiences of the past, she trusts they will continue to guide her into the unknown yet boundless future.

Big Battle is a one-shot OVA set after the climax of the original Votoms storyline, but before the epilogue at the end of the series itself. With the Gilgamesh and Balarant forces still trying to advance their PS programs, Chirico and his old friends are forced into one last gladiatorial battle against a special PS and a formidable land battleship.

Aki Tesno lives in a poor village at the bottom of a valley. One day, a man from an uptown city asks Aki to rescue a kidnapped girl.