The Promise of Chang’an.

Helan Mingyu, a bright young woman, forms a deep bond with the 9th Prince, Xiao Chengxu. Though they develop mutual feelings, fate intervenes—news of Chengxu’s death on the battlefield forces Mingyu to marry his older brother, King Xiao Chengrui. As Chengxu achieves military victories that strengthen the kingdom, Chengrui grows increasingly jealous. When the truth about Chengxu's mother's death emerges, Chengxu sets out to claim the throne and seek justice.