Ai Sunakawa (砂川 愛, Sunakawa Ai) is Makoto's older sister and a college student. Takeo mentions that she, like her brother, is a great and kindhearted person.
She is very beautiful. She looks a lot like a female version of Suna. She has long wavy red hair and wears very stylish clothing that compliments her figure.
Like Suna, she is a kind person. While a calm person, she is more in tune with her emotions, becoming emotional fast and being a very expressive person in general. a very intelligent, observant person like Suna. Also hinted that she has crush on Takeo but she doesn't appears it on other hand he just sees her as friend's sister and sometimes asks her for advice While somewhat confrontational and harsh, she is actually a very sweet person who looks out for others, especially those she cares for and is extremely helpful and selfless. She is also very responsible, not liking it when others slack off and scolding those who she feels need to get their act together.
She is Suna's older sister by three years. Her father was worried when she was born because he had a weak heart and hoped she would be okay. When he learned she was born healthy, he was ecstatic. She grew up in a loving home. When Takeo was younger, Suna's sister would treat him like family and watch out for him, telling him his clothes were backward and wiping his face.
When she was younger, she was tall and thin and compared to an ugly statue called "the Image of the Growing Child" which was at the courtyard of her elementary school and the boys bullied her, nicknaming her "The Growing Statue Girl". However, Takeo didn't think she looked like that but instead believed she looked like a white lily (he didn't know the name of the flower but pointed to it) and that she was beautiful. At that moment, she developed feelings for Takeo. She decided to wait until he became a university student to confess her feelings due to their age gap, but before that time could arrive, Takeo had already begun dating Yamato.
Makoto - Although they're related and share some physical characteristics, Makoto is almost the polar opposite of Ai personality wise. Makoto is often calm (practically indifferent), and seems emotionally distant, while Ai is more in touch with her feelings and is more outspoken. Nonetheless, the two are close. Ai likes to boss her younger brother but loves him and he cares for her as well and acts as her confidante regarding her feelings for Takeo despite him being Takeo's best friend because she knew he wouldn't tell Takeo. He does however tend to find her annoying when she cried and shook him but still helps her through her feelings. It is interesting to note though that he didn't know she had a crush on Takeo considering how observant he is though it could be he didn't expect it and saw her actions toward him like an older sister and/or she hid her feelings well.
Takeo - Ai has always been a big sister figure for Takeo, ensuring he's dressed properly in public and not forgetting anything important. It's revealed that she has been in love with him for a long time, ever since Takeo was in third grade. When she discovered that Takeo actually has a girlfriend, she was in shock from a combination of disbelief and jealousy. Unbeknownst to her, Takeo also had a crush on her as a child, but she didn't realize this until much later.
Yamato - Ai is initially suspicious of her, thinking that no normal, pretty girl would be interested in Takeo without underlying reasons. After some misunderstandings were cleared, she understands that Yamato is just as naive and caring as Takeo and approves of their relationship, in spite of her own broken heart.