natural expression of one's true self; unaffected sincerity
A yojijukugo describing the natural, unpretentious expression of one's genuine character or feelings, often with a nuance of innocent frankness.
His unaffected sincerity made those around him open up.
Her smile, a natural expression of her true self, was very striking.
天真爛漫 emphasizes innocent, childlike purity and cheerfulness, while 天真流露 focuses on the outward expression of one's genuine inner nature.
A yojijukugo combining 天真 (natural innocence) and 流露 (expression, revelation). The exact historical derivation is uncertain, but it is conventionally associated with the idea of one's true nature being revealed naturally.