Keiichiro Katsuragi is a man of tradition, who is from a super elite family whose grandfather and father are both former Prime Ministers.
 What's more, the Katsuragi family has a "tradition" 
 ~! In which boys are not allowed to have any sexual contact with girls until they turn 18!? !~

His rule: No sexual relations until age 18! Her rule: No rules.
 
Free-spirited Yuri Hasegawa and straitlaced Keiichiro Katsuragi have fallen in love. But his elite political family—which has produced a long line of prime ministers—does not allow male descendants to engage in any sexual relations until they are 18. Can the physically affectionate Yuri and rule-abiding Keiichiro keep their relationship strictly chaste?
 
Yuri and Keiichiro have gotten to know each other on their daily commute to their respective high schools. Yuri makes a passionate love confession to Keiichiro, and he feels the same! As a new couple, Yuri rushes in to kiss her new boyfriend, but...!
 
(Source: VIZ Media)