I am looking for a story I read here or on fictionmania.

It was about a boy who lives in a world where mankind is battling spirits, demons, or aliens.

They are tested as children to see if they have an ability to use a special energy.

The 4 types of energy are fire, water, earth, and wind

and this boy is an anomaly a boy that tests as a water, when usually only girls test that way and boys test for fire.
he is given a choice of activating himself since they do not know what will happen.
when he activates by fitting one of the enties he turns into a girl.

He is the strongest water user ever but weak in all other forms at first.
As she fights the enties she gains supper affinity with the other forms.

I am looking for that story if that is not enough info I know more details, I just dont want to ruin the story for people who have not read it.