PROMISE

The House of Nytheris had stood tall among the other houses for its cruel and malicious upbringing. Sein, born a boy, means he will always be at the front of the door to death. Knowing this, his parents chose to swap him with his twin sister. Living in the house as a girl is better for survival. He grows his hair and wears a dress while her sick sister was raised in the countryside. No one else knew of this secret. She is Siren, a girl.
At the end of the day, his rebellion towards the family succeeded. He rises as the head of the family, finally appears as Sein, and people start to cower in fear at the sound of his footsteps. However, fate chose to play with him; his old childhood friends came home from studying abroad.
Upon the news of Siren's death, they come forward and demand the truth from Sein, not knowing their presence pulls Sein into his nightmare he don't wish to revisit.