"I decided a long time ago that I would tell you once we turned 18."
"Marry me."

The day before high-school senior Nino turns 18, her handsome and extremely popular childhood friend, Ichi, proposes to her. Practically raised together as siblings, she can't believe his feelings and turns him down. He quickly counters with, "Let's do an experiment to see if we can be in a relationship or not"...?!

From then on, he hugs and dotes on Nino no matter where they are, and schemes on how to get her all to himself.

"Can you be mine and mine alone already?" But things aren't as simple as he hoped. When you're head over heels for your longest and closest friend, even the sweetest of love has a lot on the line!