にちゃっ

にちゃっ, にちゃあ, ニチャァnicha

adverb · noun

  1. making a creepy, slimy, self-satisfied grin
  2. smirking in an unsettling way

Study it in Yanamino

Data from JMdict, KANJIDIC2 (EDRDG), KanjiVG, CC-CEDICT and Make Me a Hanzi. Sources and licences