Hirahira to Gunjou
ひらひらと群青
Kasumi is a popular and happy student admired by her peers, though she keeps hidden a butterfly-shaped mark on her ankle. Naoshi, a melancholic and isolated boy, was her childhood friend and is the sole person aware of her secret. They have not communicated for years, and despite Kasumi's desire to reconnect, Naoshi deliberately stays away.