A love-struck brotherly love
He was his biological brother, but he actually killed his biological parents in front of him, which made him only full of fear and hatred towards him.
He hates him, he feels that he imprisons himself and even violates himself regardless of ethics just because he is dissatisfied with his own desires and wants him to collapse.
Unexpectedly, in this gradual love affair, he found that he actually fell in love with him - his own brother...