This is the 2968th most frequent Japanese word.
スー
"スー" is a Japanese onomatopoeic word often used to represent a soft, smooth, or gentle sound, like the sound of inhaling or a light breeze.
スーっと refers to something smooth, clear, or refreshing, often describing a state or feeling of relief or clearness.
私はこの風景が好きです、特にスーっとした青空。
I like this scenery, especially the clear blue sky.
スーっと in this context describes the smooth and unobstructed feeling or action of something affecting someone emotionally.
彼女の言葉が心にスーっと入ってきた。
Her words smoothly entered my heart.
スーっと is used here to describe the quick and smooth manner in which an action, such as the passing of wind, occurs.