Watch her when I can't. You're the only one I trust."

Those were the words that sealed Yuto's fate. An orphan with no last name and a reputation as a street rebel, Yuto never expected to find a home. But when he saves Lulu Gardner from a dangerous confrontation, her overprotective older brother, Shay, grants him the ultimate honor: he becomes Lulu's personal guardian.

Shay sees Yuto as a brother-in-arms. Lulu sees him as the boy who finally looked past her "princess" exterior.

Lulu is determined to break through Yuto's walls, embarking on a month-long mission to win his heart. But for Yuto, loving Lulu is the ultimate betrayal of the only man who ever treated him like family.

As they fall into a "Double Life" of secret dates and whispered promises, the shadow of Shay's trust grows heavier every day. In a world of loyalty and lies, can their love survive the moment the shield finally cracks?