Umi is no stranger to the fact that, often times, the world is simply a cruel and unjust place. When she was a young girl both her parents were taken from her, killed by a petty thug who broke in to their home to rob them. Umi was devastated by the loss of her parents, but she tried to stay strong, her situation was hardly unique after all. Umi came to realize this when she was sent off to live at an orphanage. Abuse, neglect, abandonment, untimely deaths... So many of the other children there had lost their homes, had to suffer, just like her, through no fault of their own. What's more, Umi knew things were like this the world over, terrible things happened to so many people for no discernible reason.
The world wasn't fair. There was no such thing as justice. Awful things happened to innocent people and evil people rarely ever got what they truly deserved. Umi harbored these feelings in her heart as she grew up and, gradually, she secretly to came hate this unfair world. Deep in her heart Umi began to think to herself that it wouldn't be so bad if an unjust world like this one were to just disappear.
Not long after she came to these conclusions, however, Umi encountered her Tsukaima. Presented with the opportunity to become a magical girl Umi was overjoyed. With the new power she was gifted with Umi saw her chance to make a difference, justice may not exist in this unfair world, but now she could create her own. Umi began to use her power to help those in need, to stop senseless violence, to punish the criminals who would otherwise walk away. For a time Umi truly felt that she was making a difference and those resentful feelings in her heart, that dark desire for the end of everything, faded in to the back of her mind. She felt happy.
That feeling wouldn't last however. One night while Umi had snuck out on magical girl business her orphanage fell victim to an arson who set the building on fire. By the time Umi finally returned it was only to find fire crews and ambulances surrounding the burned out remains of what had now been her home for years. Many of the other children, some whom she'd known ever since she was orphaned, had died in the fire, killed in their sleep. Umi broke, she fell in to her own despair as she realized that no matter what she did, no matter how hard she fought to bring justice to the world, it would never be enough. Things like this would keep happening, the innocent would needlessly suffer, just like her friends, just like her parents, just like she had.
The world wasn't fair. There was no such thing as justice. Umi told herself once again, the feelings she had tried to repress returning to her with force. She just wanted this awful world to end. As she finally went to sleep after that awful night Umi was struck by a terrible nightmare. She saw a Youma, one more massive and powerful than anything she could have ever imagined, materialize above Tenkawa City, reducing it to rubble and ashes in moments. She then watched as it set off in to the distance, leaving nothing but complete and utter annhiliation in its wake. That was what she needed she thought to herself. With that Youma she could finally bring an end to this cruel world.