18-Sai, Biji Kon Hajimemasu.

A rookie wedding planner enters into a contract marriage with her first love's younger brother?! 18-year-old Mashiro Isshiki is about to join her father's company, Isshiki Wedding! Her dream of becoming a wedding planner has come true, and her first love, Kanae, who she has always been in love with, celebrated her graduation and joining the company. She couldn't be happier! But her happiness gradually crumbles after her father, troubled by the company's debt, attempts suicide...! If she doesn't change, she won't be able to protect the people she loves! Mashiro accepts marriage to Kanae's younger brother, Takayoshi, in exchange for protecting her father and the company. As she grows as a planner, facing Takayoshi's constant challenges, will she be able to finally achieve her dreams and love?

(Source: Shueisha, translated)