This is the Anima Arma of Amoena's soul. The name translates to Fairy Queen.
Anima Arma are weapons that the user can materialize from their own being. Their forms can change, but only under special circumstances. This is usually caused by a shift in karma or emotions.
Karma Shifts and Emotional Shifts give different outcomes and are different in the way they work. A Karma Shift is a dramatic change and can even render the weapon unusable or change it into an entirely different weapon. Emotional Shifts are temporary and are achieved by concentrating on a specific emotion. An Anima Arma usually only has one Emotional Shift.
Furthermore, Anima Arma can be rendered unusable if the user's soul is lost, becomes damaged, or under extreme emotional stress.
Now, enough boring explanations! c: