Grandpa Pulled Some Strings, So I Took Over the Ghost Post Office from the Start

[Original, not fanfiction; wild imagination; wish-fulfillment] Supernatural forces are returning? Chu Jie isn't worried! His grandfather pulled some strings for him and even left him a deluxe starter pack.

He starts out owning a ghost post office and awakens the sequence [Arrogant Heir]!

He smashes the world's unjust rules, recruits eerie creatures as servants, and roams between the realms of yin and yang, putting anyone who dares defy him in their place!

When the eerie creatures knock on Chu Jie's door, they'll face a “spoiled young master” even more unreasonable than the fiercest ghost, backed by a steadily expanding... supernatural empire! (The protagonist has subordinates and his own faction. He charges in when he should and keeps a low profile when he should, with some behind-the-scenes elements.)