Meaning:
“黑” means “black,” but also can mean “sinister,” and “化” means “to turn into.” This term, originating from Japanese anime “Fate/Stay Night,” refers to scenarios where a character who started out as kind and innocent gradually becomes cruel and evil, often after undergoing traumatic experiences.
Example:
A: 你还在追那个科幻剧吗?
Nǐ hái zài zhuī nàge kēhuànjù ma?
Are you still a fan of that sci-fi TV series?
B: 不追了,因为我喜欢的女主黑化了。
Bù zhuī le,yīnwèi wǒ xǐhuān de nǚzhǔ hēihuà le。
Nope. I stopped watching it because the heroine I liked has turned into an evil person.