We Started a So Sweet Newlywed Life.

Riko Hanae, the most beautiful girl in school, proposes marriage to me, and before I know it, we're living together as newlyweds.
But don't get carried away. This is a contract marriage.
I asked her why she was so devoted to me.
She puffed out her cheeks and said, "You're so naive, Minato-kun…"
Wait… this is a contract marriage, right…?
This is a love comedy that begins with a zero-day marriage that just goes on happy ever after.

(Source: Shueisha, translated)

Note: Includes 3 extra chapters.