扇ちゃんにJKっぽいことをさせたかった。
関係ないけど前あったリア友との会話↓

(終上の挿絵を見ながら)
私「この扇ちゃんの笑顔…どう見てもヒロインだわ」
友人「どう見ても黒幕の表情だと思うぞ」

This makes Ougi seem more like a high-school girl.
It's not related, but here's a conversation with a real-life friend↓

(While looking at Owarimonogatari 1's illustrations)
Me: "From this Ougi-chan's smiling face... she's the heroine, no matter how you look at it"
Friend: "I'm pretty sure she's a scheming chess master, no matter how you look at it."