My Handsome Target

The Red Demon.
A beautiful assassin is hired to kill the Devil.
She can be compared to a snow leopard. She's living, hunting, and killing alone.
Love is an unknown feeling for her. That feeling has been killed since she was a helpless little girl. But now she's not helpless anymore.
Now she's heartless, and nobody can hurt her anymore.
She's been building walls so big around her heart that now she's not sure that she even owns one.
But are those walls big and strong enough to keep the Devil away?