Hirasaka Hinako ga Ero Kawaii koto wo Ore dake ga Shitteiru.

比羅坂日菜子がエロかわいいことを俺だけが知っている。

Eight years have passed since they promised the witch to keep loving each other. It's a silly little naughty love story where adolescent childhood friends secretly observe each other and the coming fate that could result from their love.