Kokoro Sasaki is an elementary school student who lives in the same neighborhood as the protagonist Jahy. She first meets Jahy in a park when she notices Jahy searching for something and immediately offers to help. Kokoro possesses a pure and innocent personality paired with a genuinely kind heart. She is trusting and easily impressed, readily believing Jahy’s account of magical gems and expressing excitement that Jahy can transform. Her primary motivation is to bring happiness and good luck to Jahy; unable to find a gem, she instead gifts Jahy a four-leaf clover as a token of encouragement. In the story, Kokoro serves as a supportive friend, consistently offering praise and warmth that gradually compels the initially aloof Jahy to open up and form a bond. Kokoro’s kindness and sincerity help humanize Jahy and play a role in Jahy’s adjustment to life in the human world. She is also described as a bit scatterbrained but honest and cute. While Kokoro does not possess any magical abilities, her notable trait is her capacity for pure-hearted generosity and empathy, which positively influences those around her. Her own character remains consistently kind and supportive, and her influence is seen in how Jahy begins to appreciate genuine friendship.