“Mounting” is the greatest ranking system that has been passed down since ancient times. Wealthy children gather at Sakurano Private Academy under an absolute rule, to take the mount and climb to the top. An ordinary student, Sato Rei, is on the verge of being relegated to the lowest class and spending three years being bullied by the rich. The only way to survive is to move up to the S class. A beautiful girl named Tsukinami Senri appears and kisses him, saying “Become my lover to take the Happy Mount!” “Why!?” Together with the most annoying girlfriend ever, he aims for the top of the school!