前に描いた妹さん（pixiv #25083680 "»":[/posts?tags=pixiv%3A25083680]）の中学生の頃。　　　この頃はまだ清い関係な設定。

Previously drawn younger sister（pixiv #25083680 "»":[/posts?tags=pixiv%3A25083680]）during her middle school years.
During this time, the setting is still of an innocent relationship.