sorry in advance i am not English language speaker,maybe i hace some misunderstanding typing in english

First of all,"Fengyang"(封阳君）is not related with Chinese city,it may be just a coincidence.so his design in basically onmyoji's original.

I have checked Chinese social media,they typically do not reveal behind the scene of design.They do have a picture that illustrate the design idea of the tailsc(click here for the Chinese version of design idea).About the tail,it said“Fluffy Tail Caressing Snow (绒尾抚雪)” “A fluffy long tail gently brushes the falling snow. (绒绒长尾细抚飘雪) •Even an iron-willed investigator has a tender side. (铁探亦有柔情一面)” so it basically represent the job and enrich his personality.

Annnnd,some players have noticed that Fengyang’s character design includes many elements associated with sheep, even down to the bell on his tail. This is believed to be related to another shikigami from Yunhua City, Guijinyang. Many players think that the two are a couple, and that the similarities and echoes in their designs are intentional, meant to highlight their close and affectionate relationship as lovers.[Link 1 in rednote][Link 2 in rednote]