Let's Do It Already!, Vol. 1 by Aki Kusaka

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?

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! Yuri rushes in to kiss her new boyfriend, but…!