Saegusa Izumi (七草 泉美) is one of Mayumi's younger twin sisters who both had cameos in the WEB Novel Arc 5 & 10, in a scene where they watched their sister make bitter Valentine's chocolate for Tatsuya and Hattori. Izumi, along with her twin Kasumi, are formally introduced in the released segments in Dengeki Bunko Magazine from an arc that features the Shiba siblings' sophomore year in called "Double Seven", when the twins both enrolled as freshman students. Izumi ranked second during the entrance examination, and joined the Student Council.