At the dinner party where Lu Xu was named the youngest general in the empire, Ding Ying'an accidentally entered estrus in front of Lu Xu and seduced the drugged Lu Xu.
Imperial law stipulates that when an Omega meets an Alpha during estrus, it does not mean that the Alpha can release his sexual desire and mark the Omega at will. If it is later found out that the Omega was not voluntary but was marked for life, Alpha may pay a huge sum of money and be imprisoned.
Ding's father forced Ding Ying'an to marry Lu Xu and wanted to use Lu Xu to support the Ding family company, which had recently been unable to operate financially. He even threatened Ding Ying'an with the relics that Ding's mother left for Ding Ying'an during her lifetime.
Ding Ying'an and Lu Xu reached an agreement to become an on-screen couple...
Purpose: live a good life