I place her around 3 years older than Sasaki, but the Japanese educational system eludes me (the Philippine system is just basically 6 years elementary, 4 years high school, 4 years college). So middle schooler Sasaki would have a nee-chan in 1st year high school, I'm guessing.

  

Um, so there. (Click on it to enlarge) Anime/Manga genetics are very unique, aren't they? And it's amazing how anime/manga characters can maintain the same hairstyle they've had since they were kiddies. And yes, middle schooler Koutarou is wearing a printed violet undershirt, because he *can*.

Anyway, I thought of making her an 80's kid, because, well, I dunno. Koutarou's all 50's, I thought it wouldn't hurt to try a different era. But when I started drawing her, she just ended up becoming 50's herself, I probably was influenced by Grease and Hairspray... I wanted her originally to be cute, but she ended up fierce (I also wanted her to look like Koutarou if ever he were a girl), and so I just went with it and drew a slightly scared middle schooler Koutarou. 

So I'm thinking, hell, she pro'lly went to Zokugaku as an old school female yankee/delinquent student, haha, and was Rui and Megu's sempai. 

She dotes on her younger brother but thinks he's kinda stupid, and would occasionally enjoy scaring him. She likes Juri as well, but is unimpressed with Akaba (making her probably the 1st female eluding the Akaba charm, gasp). She hasn't been watching Koutarou's games because she thinks it will conflict with her loyalties to Zokugaku, and waits for her to graduate before fully supporting her younger brother's football career. 

I was thinking of doing Akaba's younger sister, but Akaba eludes my drawing pen, I just can't get the Es21 art style.