Aqua was originally a keyblade master but after helping her friend to defeat his darkness and destroy the x-blade that same friend was put into a long sleep. She then went to save her other friend who was possessed by master xehanort but in thinking she saved him. She pulled him out of falling to the realm of darkness but she’d fallen into it instead. After years of surviving and fighting for her life she’d had survive for 12 years only until she was hit by darkness and she had fallen.