Save Rei while it's foggy with 〜うちに

Grammar Explanation: During with 〜うちに

Jadeite captures the priestess Rei. Ami uses an ability to fill the area with fog, giving Usagi a chance to act.

亜美(あみ):: 「うさぎちゃん！霧(きり)が出(で)てるうちにレイちゃんを助(たす)けて！」; "Usagi! (Take the opportunity to) rescue Rei while it's foggy!"