Eh, if you don't think race-based xenophobia isn't usually real you need to read more pre-modern history. Even pre-Christian Roman commoners have been racist to Roman citizens from other parts of the Empire.
It is a stretch.
Although, it takes 21 days to develop a habit. MC was a dog for two months until he found Inari.
So IMO it is just enough if you suspend your disbelief.
To those who think she did it because Kyosuke thinks she gained weight:
Hori clearly states that she did it because she did not want to be the same weight as her boyfriend. It's not a matter of being fat.
"invention"
In other words, something that is discovered, learned and/or created.
Which means there was a time when it did not exist, and it could be lost.
Congratulations, you've played yourself.