Mikan Yuuki  

, 結城 美柑

Rito's 11-year-old sister Mikan takes care of the housework while their parents are away on business. Unlike her brother, she is very mature and does not hesitate to tease him, even going as far as saying they are not blood related just for a laugh. Despite this, Mikan seems to have a certain lack of respect for Rito because of it. However, when he develops a fever, she addresses him with the honorific "Onii-chan" and thanks him for trying so hard to take care of her. Although Mikan may not show it, she deeply cares for Rito and misses his company. She grew attached to Golden Darkness perhaps because they are both around the same age. Mikan is very perceptive and can read people's emotions and reactions, including Rito's obvious anxiety around Haruna and Yui.