From Genshin Impact

In Heizou's youth, he was rebellious and disliked following rules. Despite calling himself a detective and serving the Tenryou Commission, his investigations revolve around his personal principles and appear to be unrelated to any governmental duty. Heizou's view of the term "detective" mostly stems from his belief that one should be evil's natural enemy, as the damage had already been done despite any attempt to cover it. This caused him to split with Sango.