To add on an example of a character being marred by the author’s other work, perhaps the most infamous contender would be Haguhagu’s Sasha. Sasha and her Otaku Classmate is a relatively wholesome romcom and something of a coming-of-age story. Unfortunately, let’s just say that b4 writing this manga, Haguhagu created Sasha for some… less than wholesome reasons. The degeneracy of Sasha H includes tags like:
Fat Ugly Bastard
Dubcon
And other morally dubious things
On one hand, this gives Sasha a lot of unique lore and backstory that fleshes out her character. On the other, it makes the manga sequel rather problematic and tough to chew on, knowing what else the character Sasha has done. I do respect the artist’s balls to use the exact same character, completely unchanged from H version in personality or appearance, and only slightly changing her backstory to make it less fucked (But I have heard the manga raws shows some weird shit still stays). They are the most egregious example of a H turned licensed manga in current existence. Reddit link to other H turned manga here from a few months back.