Recorder and Randsell(リコーダーとランドセル)

"Recorder and Randsell" is an anime television series based on the 4-panel manga series by Meme Higashiya. The story revolves around Atsushi Miyagawa, an elementary school student with the appearance of a full grown adult, and her older sister Atsumi, who conversely looks young despite being a high school student.