Tomoko Saeki, Shun Saeki's younger sister, resides in the same apartment building as the main characters. She radiates the same inherent cheerfulness as her brother, perpetually wearing a smile regardless of the situation. Tomoko playfully engages with Okojo, readily handling the ermine and even using him as a makeshift scarf during their fun. Her fundamentally jolly disposition means nearly any event or sight can easily provoke her laughter.