One summer day, freelance illustrator Kouichi received a mail while drawing at home like usual. It was a request from his relative to take care of her daughter Kanon for a few days. He didn’t want to be distracted from his recently acquired work, but he quickly changed his mind when he opened the attachment and an angel smiled back at him. The week passed quickly and she grew fond of him since he was nice to her and she always wanted an older brother. Afterwards, she still came often to his place to play, bringing along her friends Yuzu and Shiori. One day, with the cicadas chirping in the background, she raised her skirt up to her belly. “B-Big Brother, please teach me…” Thus begins the sweet and stimulating secret pretend-love between them.