Red Rain

Emblyn, the princess of the castle tower, has lived a life of scorn and ridicule, shunned by the king. Driven to her limit by the king's violence, she dreams of freedom, and one day, at the queen's behest, she sets out for the Redian territory. However, powerless and alone, she impulsively writes a letter to Triss, the heir to the Aek ducal family, asking him to be her guardian, having witnessed his devotion to her younger sister. Then, after clashing with her father over her sister's marriage, Triss runs away from the ducal family and heads without hesitation to the Winter Garden of the Redian territory, where Emblyn is staying...

"I, Triss Aek, pledge my honor before God to protect Emblyn from this moment on until death breaks my oath."

(Source: Naver, translated)