I don't know?
It contains mild insults (fuck, shit, etc.) and mild violence (fist fight, stabbings) to moderate one (fantasy amputation). There is no explicit sexual scene so far because the plot doesn't need it. In another side, while it's not explicit there is a scene of nudity (not detailedly described), self-harm, implied sexual coercion (although between immaterial beings) and abuse. The future arcs although still a far reach will include more topic that maybe needs caution, such as cannibalism, necrophilia, genocide, and rape.
I try to be as tame as possible as I don't like writing too many disturbing things myself. I feel when the mentioned topics can make it restricted, it's still in a mild extent that it can be PG too.
Maybe it would be between PG-13 and R-rated but will never reach NC-17 I think.