These two girls are Natsui and Chiaki Otani from a yuri short story I'm working on. They're a year apart. Despite being the oldest, Natsui can never say 'no' to her adorable little sister. Natsui is tomboyish, but also act mature for her age while Chiaki is girly and can be boisterious sometimes. They share the same secret, they have feelings for each other. The girls' feelings for each other changed when they're about 7-8 years old; that was the time when they share their first kiss after they caught their parents kissing. Since everybody around them see their relationship as just a normal sisters relationship, the thought of loving each other as lovers never came to mind so the girls decided to just keep their true feelings inside.
One day, Chiaki discover Natsui's secret about being into girls, and begin to open up more with how she feels to even trying to seduce her.
Base: Base 10