My Sister Drank a Suspicious Drink and Got Too Horny

A student studying at home is interrupted by his older sister, who accidentally drinks a suspicious energy drink meant for him. The drink has a side effect of increasing libido, leading her to aggressively seduce him. They end up having sex, and the next day, she visits him at school in a uniform, still affected by the drink. Yuina and her brother Itsuki continue their intimate encounter in a classroom setting, roleplaying as classmates. They later return home, where they take a bath together and continue having sex, eventually moving to a bedroom. The story concludes with the brother and sister finishing their intense sexual encounter. Afterwards, they are seen studying together, with the sister encouraging her brother to pass his exams so they can live together, promising to stock up on the 'energy drink' that caused her to go into heat.