素 is one of the most commonly used Japanese kanji, and it also has a lot of special readings in addition to the standard onyomi and kunyomi readings.
ONYOMI 音読み
もと moto
KUNYOMI 訓読み
ソ so ス su
Examples
どうやら、さっきのは演技ではなく、素だったらしい。It seems like that she wasn’t acting back then; they were her real feelings.生粋のお嬢様だからな。残念ながら悪戯とかじゃなくてあれで素だ。She’s pure bred blue-blood you see. Unfortunately that’s no sort of put-on but her natural self.そ、そうじゃなくて、・・・ 素の自分、本当の私を必要としてくれる人がいるなんて、考えたこともありませんでしたから。N-no it’s not that … it’s that there could be someone who would need me for what I am, for my true self, I hadn’t even thought of that possibility.