Kotegawa Yū

Kotegawa Yū is Yui's older brother and a ladies' man, which she dislikes about him.

Appearance
Yuu is a tall and fit young man who has light brown spiky hair and gray eyes.

Personality
Yuu is a quite calm and easygoing guy who is something of a ladies' man, but he can also be very protective of women when he sees them in trouble. He enjoys teasing his sister about her relationship with Rito, like mentioning him in front of her and their parents.

Plot
He appear the first time in Chapter 86. After finding Rito and Yui being chased by hoodlums, he beat the bad guy without being seen from her sister and the boy. Noticing Yui's interaction with a boy like Rito, he hopes Yui will grow to be more mature.

In chapter 120, he meets Rito directly when he come to their house to give Yui her homework because she caught a cold and didn't come to school. Yuu insists Rito to meet with Yui and, later, he mistake an embarassaring situation between Rito and Yui thinking her sister made much progress and this was unexpected.

Since then, he has taken notice of Yui's relationship with Rito. He can easily read his sister's poorly hidden feelings and her love for Rito, and is eager to see his sister become more open to romance through Rito. Every now and then, most of his appearance would show him teasing his sister about stuff like going on a date with Rito.

Kotegawa Yui
Yuu is Yuu's little sister. She greatly dislikes how he can be a ladies' man and how he always brings up Rito in front of her, to which she occasionally overreacts and blushes, something he enjoys teasing her about. He is aware that she has feelings for Rito and finds her very easy to read. He can also be very supportive of her sometimes. Yuu hopes that she will be more mature and accept her love for Rito.

Yūki Rito
Yuu first noticed Rito when he saw him trying to defend Yui, and has since been interested in keeping track of his sister's relationship with Rito. He would often mention his name at home in front of Yui, just to make fun of her.

After speaking with each other (and sharing a beating from Yami, due to him complementing her clothes and Rito getting into a perverted mishap), he understands more about Rito's life with aliens and all the misfortunes happening around him. He sympathizes with Rito, but remarks that at least his life is more exciting. Rito seems to like Yuu, as he finds him to be a really cool and understandable person.

He is one of several people who knows that Yūsaki Riko is in fact Rito.

Sairenji Akiho
Akiho is someone Yuu is currently dating, but she isn't taking it as seriously as he does and he feels disappointed every time she turns down his invitations with some excuse.

Etymology

 * Kotegawa means "old hand, disused article, retired official, ex-soldier" (古手) (kote) and "river, stream" (川) (kawa/gawa).
 * Yū means "play" (遊).