Voiced by: Mai Kadowaki (Ren) and Tamaki Nakanish (Ai)
Ren and Ai are twin sisters who are first-year students at Kouta's school, and first appeared in the fifth volume of the novels. They are ninja spirit hunters but are quite bumbling at it. They suffer from extreme poverty and live at a very poor temple and are frequently seen doing things that homeless people would do, for example, making stew out of trash and roadside weeds, or eating thrown-away bread crusts. Originally, they were given the task to assassinate [[Chizuru Minamoto]], but did not go through with it since she was still "only a kid", and the fact that she treated them to a free meal, which is considered as heaven to the twins. They are nearly identical except for their slightly different hair styles. They use chains when attacking, and are also seen in the anime ineffectively using explosives. They later warm up to Chizuru and starts referring to her as "Mama".