Daichi Fukumori, just starting his second year of high school, has been lying about having a younger sister in order to have something in common with the girl he had a crush on. When Daichi finally decided to tell the truth, a mysterious girl suddenly appeared and started calling him "big brother"! Daichi was surprised to see this sister, who turned out not to be a lie, but what awaited him was an even more outrageous situation! Hey, hey, I better have a talk with my......... sister before things get out of hand! (Source: Kadokawa, translated)

Ginpei Ebisawa is considered a delinquent. But that's not his true nature (maybe). As he continues his (misguided) quest to learn about himself, he meets his classmate Chigusa Somei (a monster with a desire for 120% approval) and discovers the dangerous depths of philosophy! The wheels of adolescence are now set in motion for two people with mutual interests...!