It was the last mission Xiao Ying had before receiving the Qiao family mission.
It was to kill the Burmese King.
She had disguised herself as a bayadere and gained favors from the Burmese King.
However, the Burmese King was heavily guarded and it was hard for her to action her attack. Incidentally, she met a close guard the Burmese King had. The man was this Long Ming and he hated the Burmese King equally to the core.
He later found out that the reason for his hatred towards the Burmese King was because his father was the real Burmese King, but was murdered by his relatives. After he was born, he was sent to the borders and almost lost his life. When he became an adult, he returned to Burma to take his revenge.
That was why she used her beauty to seduce Long Ming as well. After she gained his trust, they worked together to get rid of the Burmese King.