toRawHiragana = function (str) {
    return [...str].map((ch) => {
        if (ch > "\u30a0" && ch < "\u30f7") {
            return String.fromCharCode(ch.charCodeAt(0) + KATAKANA_HIRAGANA_SHIFT);
        }
        return ch;
    }).join("");
}
Convert kana to hiragana

@param {string} str Given string
@return {string} Hiragana string