Vanitas and Aqua first met in Radiant Garden. He attacked her and threatened to kill her but she managed to win the fight. Aqua attempted to unmask Vanitas but he quickly recovered. They later met again in Neverland. Vanitas mocked Aqua for treasuring Ven's wooden keyblade and snapped it in half. The two fought again and Aqua believed that she finished him off this time. However, he lived and the two later met in the Keyblade Graveyard. Ventus was frozen and Vanitas attacked Aqua in order to enrage him. She was knocked unconscious while the two boys battled. Eventually, Aqua woke up and found Ven to be possessed by Vanitas. She was forced to fight him while Ven defeated Vanitas from inside.
Vanqua is a moderately popular Kingdom Hearts ship. It is not as popular as Terraqua or Venqua but it still has a fair amount of fans. Since Vanitas is another half of Ven, some fans feel that Vanitas has just as much chemistry with her as Ven does. Some like the fact that Vanitas is dark while Aqua is very full of light and has never used the darkness. She was also later trapped in the Realm of Darkness so some like to theorize that she can see Vanitas again.