Rena Aikawa (藍川玲奈, Aikawa Rena) is one of the children abducted by the Mutagawa Group for its first human trafficking venture.
Three years prior to the start of the story, when Rena was roughly five or six years old, her father remarried. He and her step-mother, Mari, had a daughter, Arisu, and Mari began to abuse her step-daughter Rena out of spite. At some point, a neighbor called Child and Family Welfare Services after hearing hysteric yelling and crying from their home, but Rena refused to tell the agency why her face was bruised, and they had to let her step-mother go.
Rena is going to hang out at a classmate's house one day when a boy approaches her in a park. He brings her back to his apartment, where his father, a yakuza involved in human trafficking, keeps her in a closet with her limbs bound and her mouth covered with tape until he can deliver her to his organization.
Her step-mother Mari consults the Banba Detective Agency for help with locating her, avoiding the police out of fear that they will discover her history of abuse, and Zenji Banba and Xianming Lin begin going door-to-door looking for Rena in the neighborhood where she disappeared.
She is held in a dog cage in a warehouse for more than a day, crying and shaking in fear, until the cages she and the other children are being kept in are loaded onto a truck. Just down the road, however, the truck is intercepted by Banba, Lin, and Jiro Tanaka, and Lin recognizes her as the missing child he has been searching for. Banba calls the the police, and Rena and the other children are rescued.
- The name Rena means the "tinkling sound (of a bell)" (玲, re) and "apple tree" (奈, na).
- Rena's surname Aikawa means "indigo" (藍, ai) and "river, stream" (川, kawa).