Anuki: The Greatest Epic of a Young Boy(2001)

Anuki: The Greatest Epic of a Young Boy

Anuki is a boy caught in a war between two countries. When he is small he is abandoned by his father so a princess could be saved. This event triggered amnesia so he doesn't remember his childhood before this event.
When he grows up he joins a flight mercenary unit to be trained as a pilot so he can help in the war, there he becomes the ace pilot.