This imperial edict was something Xin Lin begged from the Fuzhou Emperor before she left Fuzhou.
The Fuzhou Emperor doted on Xin Lin very much. Seeing his third younger sister rarely ask for something, he didn't even think about it, just swept his brush and issued the edict.
As for what Xin Lin wanted to use it for, the Fuzhou Emperor would not interfere.
As for why she called herself Overlord, the Fuzhou Emperor would ask even less.
His imperial younger sister of Fuzhou—never mind calling herself Overlord, even if she called herself Thanos it wouldn't be too much!
Just like that, when Xin Lin returned from Fuzhou, besides bringing back an "Immunity Token imperial edict," she also came back with the title of Princess of Fuzhou on her head.
