Having a malicious or scheming nature beneath a pleasant exterior; essentially the same as '腹黒い' (black-hearted).
彼はいつも笑顔だが、腹黒なところがあると噂されている。
He always smiles, but there are rumors that he's sly and black-hearted.
取引先の担当者は表向きは穏やかだが、腹黒で交渉が厳しい。
The client representative seems gentle outwardly, but is sly and tough in negotiations.
A slang/manga usage describing someone who appears kind but is actually cruel or sly beneath the surface.
あのヒロインはかわいく見えるが、腹黒要素があって読者に人気だ。
That heroine looks cute but has a sly streak, which makes her popular with readers.
腹黒キャラはギャップが面白く、漫画でよく登場する。
Black-hearted characters are interesting because of the gap between appearance and truth and often appear in manga.