She couldn't stop smiling.
It was built on crumbling hopes and childish desires, forced across her face almost every moment of every day. It was made of rays of artificial sunlight, made of the whispers of her fallen friends and family members, made of a vow to keep going, to keep holding on to the life they had given her. Her smile was heavy and tiring, but she couldn't stop it.
She couldn't stop smiling.
Even when her family lay dead before her, she couldn't stop. Even when her classmates were no longer classmates, when they started trying to kill her, steal that life away from her, she couldn't stop. She couldn't stop because that smile was a promise, that smile was a reminder, to herself and to her foes.
She couldn't stop smiling, because if she did, she feared she might fall apart.