Ai: Hikari to Mizu no Daphne

Dahpne in the Brilliant Blue is set in a near future where the surviving population resides in underwater cities, with waterways serving as streets. Years ago, during underwater experiments, all communication with the surface was lost. With humanity now living beneath the waves, the Deep Sea 9 Cities Association stands as mankind's last hope. Ai Mayuzumi, daughter of the research lab's director, is an expert water jet bike rider. When the terrorist group Error assaults the city, Ai becomes entangled with Stelnas, a counter-terrorist group made up entirely of women and led by a girl named Kei, and she requests to join them. Initially, the group resists her efforts to join, but Ai's surprising "gift" and her adept handling of herself during a kidnapping attempt eventually win over the members of Stelnas.

(Source: Tokyopop)