I think the author reached level 99 as a hentai artist and is changing his job to a manga artist. It makes a lot of sense that he is transfering from hentai because you have to admit he is a skilled artist, but seems to be a new to manga.
The above is just a guess because I am too lazy to look up the artist right now.
Okay I guess it was originally a novel and was made into a manga, so I guess that makes sense.
@sieglhein Don't make me imagine the back issues that would cause. OUCH!