Ruka is the Cancer Star Maiden of Conception: Please Give Birth to My Child!!. She has a very perceptive insight which allows her to see into the hearts of the people around her. Ruka is the tsundere stereotype, being cold towards others, including some of the orphans at the daycare she lives at and Itsuki whom she slowly warms up to. Her cold exterior is stemmed from her being a tsukuyomi -a person who can read other peoples feelings through body contact. She also dislikes lies because she can clearly see through them and feverishly avoids being touched by anyone because of her fear of what the person is thinking. However, she is unable to understand the feelings of Itsuki and Mahiru who are immune because they are not from Granvania. Over time, Ruka learns to open herself up to other people and is more honest with them too. She also has a love-hate relationship with Mahiru. While the two are friends with each other, Ruka views Mahiru as a major rival for Itsuki's affection.