She was considered the secondary leader, other than Sailor Venus, while she acting as the decoy Princess. Even though this overwhelmed her, she was later reluctant to give the position up. She alternately admires and resents Minako's teachings about what it means to be a Senshi. She claims to hate karaoke, which the other girls love, especially Usagi, but is later coerced by Minako into posing as an idol, in order to awaken her inner Senshi. Under the name "Mars Reiko," she appears on three occasions: performing for hospitalized children, working alongside Minako, and staging a contest with Minako in order to stop her from quitting the idol business. She wanted to force Minako to realize she has friends and needs to pay attention to her life as well as their mission. She also has butt heads with Makoto. But, once Makoto discovered how Rei felt about her father, they became closer. Espeically when Makoto helped Rei escape.
Rei did not like that the past life was dictating their present lives and was resentful of all the pain the past life has caused. Even though Rei and Minako often disagree and compete with each other, they also share great respect. Minako even sometimes lets her guard down around Rei, and eventually confides to her illness and that she feels is her destiny as a Senshi. It irked Rei that Minako dismissed her own illness and mortality in order to continue fighting as Sailor Venus. In Act 34, her father tries to have Rei move back with him because an election is coming up and he doesn't want to lose face. Rei refuses and runs crying to the Crown Karaoke Studio where she spends the night with Ami, herself having just run away from her mother. Ami and Rei learned how much they had in common,e specially concerning their parents. Minako underwent a surgery due to the girls' urging, which might either cure or kill her early. Artemis arrives at Rei's temple and tells her that Minako has died. In rage, Mars rushes into a battle finishing off a Youma. In the final battle, Rei uses Minako's weapon, Venus Dagger, in conjunction with her own Mars Dagger. In the Special Act, Rei is in Kyoto, training her miko powers. She returns to Tokyo and bumps into Luna, telling her she sensed the dark power. Rei is injured by the blast of Mio's revival and is hospitalized. Makoto, Minako, and Ami try to use the Legendary Sword to get their powers back, but Sailor Luna wonders if this will work without Rei. Minako says that Rei's heart is with them, and therefore she is there. In her hospital room, Rei sees a vision of them and reaches out to them. Rei recovers and attends Usagi and Mamoru's wedding.