無口な彼の心根を知るのは難しい。
With someone as quiet as him, it's hard to know what he truly feels.
母の手紙から、息子を案じる心根が伝わってきた。
The mother's letter conveyed her heartfelt worry for her son.
強がってはいるが、その心根は寂しさでいっぱいだった。
He acted tough, but deep down he was full of loneliness.