The King's Sword Crusade, Book 1

lukan Drackous, was sent to war when he was just seven years old. There he met a woman who had given birth to a newborn girl and died due to childbirth and her multiple injuries.

Eighteen years later Lukan Drackous raised the baby and named her Luana.
He saw her as a sister, but she Luana saw him with different eyes.