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--producing a 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? 
December 25 is Keiichiro's birthday, and Yuri has been hard at work at her part-time jobs in order to throw a lovey-dovey, sexy, super-gorgeous birthday party for Keiichiro--that is, until he tells her not to bother! Christmas is supposed to be a time for couples to celebrate together, but it seems there's only trouble on the horizon!