Quick answer
Yui is a girl name.
Meaning and history
From Japanese 結 ( yu ) meaning "tie, bind" or 優 ( yu ) meaning "excellence, superiority, gentleness" combined with 衣 ( i ) meaning "clothing, garment". It can also come from stand-alone 結 ( yui ) using a different nanori reading. This name can be formed of other kanji or kanji combinations as well.
Notes and context
Usage: japanese | Japanese Hiragana: ゆい; Japanese Katakana: ユイ