A B-rank agent and the leader of Nasu Squad.

Rei is a rather quiet and sickly girl, as she is often shown sitting in bed. However, despite her frail appearance, she is strong-willed when in battle and maintains a rather calm front when under pressure, as she was able to garner 3 points for her team even though the odds were stacked against her. She also highly values her teammates, seeing as they were her primary driving force during the rank battles.