Zhang Chi had three good reasons to help Long Yan.
By killing the other demon, he would ensure his own safety.
For Hua Long Palace, Chong Xu's death was not the issue; the appearance of a demon was the real problem.
As long as they dealt with the demon, they would eventually back off.
By killing the demon, Zhang Chi could also gain experience in dealing with the Demon Clan, giving him the confidence to face Second.
The third advantage was associating with the Wealthy Woman.
Of course, Zhang Chi had no intention of using his charm to deceive Long Yan. He had one million (dollars), and there was no need to get involved in a romantic drama with an older ugly woman. Being friends was enough.
Later, when he went to develop in Hua Long Palace's realm, he would have an additional connection.
But dealing with such a rich and confident woman, flattering her would be useless. What Zhang Chi needed to do was to simply and crudely break through her defenses.