Sana Kaizu is Takumi's younger stepsister, one year his junior, sharing no blood relation and living together in the same household. A high school student, she habitually struggles to wake up on time and requires morning assistance despite her age. She stands 148 cm tall with measurements of 76-52-80 cm, sporting light orange shoulder-length hair styled with an ahoge and ribbon accessory alongside blue tareme-shaped eyes. Energetic and active when awake, Sana occasionally displays clumsiness. She frequently initiates activities and rallies friends to participate. Her best friend Chiwa Amano is nearly inseparable from her; their constant companionship highlights how Chiwa's unpredictable nature contrasts yet complements Sana's liveliness. Within family dynamics, the absence of blood relation positions Sana among Takumi's potential romantic interests in the story. Her attire includes a sailor school uniform, hoodie, yukata, beret, and old-type school swimsuit. Her birthday is August 31.