Crunchyroll made an inappropriate tweet... and I don't get it

Crunchyroll, one of the biggest and most famous publishers and translators of Japanese anime in the west, recently came under a lot of heat from the woke left because of a tweet they posted:

They quickly had to remove the tweet and post an apology:

The thing is... I honestly cannot understand what's so insensitive and inappropriate about the original tweet. It was a translation of something written in Japanese... and it was somehow so insensitive that they got a huge amount of backlash.

Which part of it, exactly, is insensitive? Is someone "becoming a dark-skinned gal" insensitive and inappropriate? This is a fictional cartoon. Is the cartoon itself inappropriate because someone in it "became a dark-skinned gal"? Why is that inappropriate? Is it inappropriate for Crunchyroll to say that? Why?

Or is, perhaps the inappropriate thing the possible implication that dark-skinned girls are promiscuous?

I thought that the far-left was not only A-ok with promiscuity (just look at "pride parades"), but in fact encourage it. Second-wave feminist sexual liberation of women taken up to eleven, and all that jazz. But in this case it's inappropriate to make it sound like "dark-skinned girls" are promiscuous?

If that's the problem, then it once again demonstrates how impossible it is to abide by the ever-changing fleeting rules of the far left. You can never, ever know if something is considered "offensive" by them. If you say that girls shouldn't be promiscuous, you are being an offensive bigot. If you say that girls are promiscuous, then you are being an offensive bigot.

Or is the problem that "dark-skinned" girls must not be implied to be promiscuous? So there's nothing wrong with promiscuity... except if it's "dark-skinned girls"?

I'm completely confused. I don't get it. I would be a really bad "ally" because I simply cannot comprehend all these contradictory rules and principles, and I could never predict what is "offensive" to them.