Yui Mizushima

Iku's twin sister. She has very little screen time, always seen being sickly. She can't even frequent school due to her illness and weak constitution. Yui and Iku are very close. The two twins grow up together Kotaro Hoshizuki and they were used to call him "Kouta-nii."

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At some point, she confess her love to Kotaro, but she is rejected. She later dies. She dreamed to become a teacher and his brother will be convinced by this and will realize her dream at her place.