An ex-yakuza who has lost his way finds a new life working for a mysterious florist whose shop only opens at night. After being released from prison and losing everything, former yakuza Kaoru Mitsuya was wandering the entertainment district when he came across Yuuichirou Shirouzu, a flower shop owner who had collapsed in the street. After helping him, Kaoru ends up working as a live-in employee at the shop, marking the beginning of a new life and a new love.

The story, set against the backdrop of a quiet city at night, follows Kaoru and Yuuichirou as they navigate their budding relationship. The original series ends with Kaoru, who fell in love at first sight, finally having his feelings returned by the reserved florist. The sequel, Mitsubachi to Lemon Balm sweet moment, begins with the two now living together as a couple. Their days are filled with happiness, yet they struggle to cross the final physical line. Neither wants to break the precious happiness they have found, but both cannot deny their desire for the other.

Their tender and frustrating time is complicated when Kaoru encounters a mysteriously alluring man named Yuzu, who takes a liking to him, adding a new layer of tension to his relationship with Yuuichirou. The story follows their pure love as they confront their pasts, learn to trust, and deepen their bond.