Reirei was characterized by an adventurous yet pure mindset that drove her to make the move from Mt. Kaou to the outside world. Spunky, brave, and crafty, Reirei's big personality made up for her small stature.
Her parents died when she was young and she was left in the care of her brother, Kieron. Mt. Kaou was all she knew but she longed for a new life with purpose and away from her brother.
She also owned a magical long staff that she could lengthen and shrink at will. It appeared as a simple hairpin when it was not in use. Being raised as a bandit provided her with combat training and her strength was demonstrated multiple times in the novel.
- "Hm. It's an honor wound."
- —Reirei, Genro Den Chapter 7
She first appeared when her brother was in the middle of torturing Tasuki. After scolding Kieron for his disgusting behavior and untieing their prisoner, she took Tasuki back to his cell. He thanked her for saving him and then ordered Kouji to tie her up and take her as a hostage.
It took the bandit duo a bit of squabbling before they realized that the treasure they were sent to take was Kieron's own sister. Not seeming to struggle against her fate, Reirei was carried through the stronghold until they encountered a room full of Kaou bandits. Surprisingly, Reirei enthusiastically directed the two boys to a secret exit. The trio escaped and took refuge in Tasuki's old home.
Once there, Reirei was allowed out of her bonds and developed a bond with Tasuki's family. That night, she caught him outside his home watching the stars. He said he wasn't a "romantic guy" to which she agreed and complimented his family. She revealed her backstory and explained that she planned on leaving with the two bandits the moment she saw them and threated her brother with a "slow and painful death" if he tried to get her back.
The next day they arrived back at Mt. Reikaku and Reirei was presented to Hakurou. Kouji lied about how they kidnapped her and told his leader that she put up a tough fight. After ogling at the Tessen, she watched as Hakurou appointed the two bandits his successors and they retired for the night. Hakurou made Tasuki room with Reirei because he "hated women" and she expressed that she hoped Tasuki would be the next leader.
In the morning, Tasuki caught her practicing bōjutsu and noticed the staff's magical abilities. To prove herself, she challenged passersby and scared them off just by lengthening her weapon at will. For two weeks, she tagged along with Kouji and Tasuki on their toll runs and did most of the work.
When Kieron stole the Tessen in exchange for Reirei, they took her to the base of Mt. Kaou. Tasuki suspiciously stopped halfway there and the girl confessed to Kouji that she wanted to join the Mt. Reikaku bandits. Kouji, who developed feelings towards her, almost agreed but he reminded her that they needed to get the Tessen. Seeing she was upset, Kouji told her the truth about Tasuki's destiny and they couldn't be the trio she wanted them to be.
Once at the Mt. Kaou stronghold, Kieron turned on Kouji. Reirei pulled out her hairpin and threw it to Tasuki, who lept out of nowhere and defeated him. But Reirei sensed something was off and claimed that it was not her brother. Suddenly, fog filled the room and a disembodied voice spoke to them. They realized the Tessen "Kieron" had held was an illusion and everyone in the stronghold was missing. Pondering over the occurrence, they went back down the mountain and Reirei suggested they get something to eat in Souun.
A few nights later, Tasuki informed her of an upcoming battle between Ougi's army and the capital. Between him and Kouji, whoever played a bigger part would become the leader after Hakurou. To this, Reirei said that she would want him to take up command so that he would stay with the Mt. Reikaku bandits instead of becoming a Celestial Warrior. On the day of the battle, Ougi did not attack, rather, the Kaou bandits. Tasuki warmed Reirei to stay put but she ignored him and fought alongside the bandits. When she was wounded, Tasuki bandaged her arm and he promised he would act as her brother. Kouji, having walked in on their embrace, grew jealous. But the battle was won and Kieron's life was spared.
Then, wanting Tasuki to become the leader, Reirei escaped to Ougi's palace in Souun to bring back the Tessen. But apparently, Tasuki got there before her and tricked Kieron to give him the iron fan. Only it wasn't the real Tasuki but a youkai possessed by Kyouan or the demon Dokoro. Reirei tried to dodge her attacks but the demon's weapon pierced her chest. Still, she fought her off with her long staff before she seized the Tessen and threw herself out the window to save the sacred item from her foe. The real Tasuki arrived with Kouji and saw her fall. The Celestial Warrior tried to reach her before she hit the ground but missed. With her last breaths, Reirei confessed her feelings for Tasuki and made him promise that he would serve the Priestess of Suzaku when the time came. In return, Tasuki vowed to avenge her.