Fukushu Kareshi: Dekiai Shacho no Kao ni wa Ura ga Aru

Both fake marriage trope of childhood friends coming together for some grander reason as an adult couple.

Soft spoken FL
hopelessly in love ML

Usokun is a little better of a watch though, even if its harder to find as the supporting cast is really great and the story relies more on the characters internal struggles (while keeping them likable while Fukushu tends to rely on external conflicts to drag the couple together.

Shirai Yui has decided to take a new job as a secretary at the law firm of her childhood friends, the Kami brothers. Yui has feelings for her older brother, Soichi, but when they meet again for the first time in 18 years, she is confused to find that Soichi has become a cool, unsmiling man. Meanwhile, her younger brother, Yushiro, has always loved Yui, but has not been able to express his feelings. And Soichi has been unable to express his love for Yui due to a childhood trauma. The love stories of Yui, who loves Soichi, Yushiro, who loves Yui, and Soichi, who is jealous of Yui's close friend, all intertwine.

One night, Kaede is accidentally locked out in the hallway at work. Shioya, who she has a crush on, just happens to pass by, resolving the situation, and she ends up staying the night at his house!? However, Shioya's roommate Mizoguchi comes home and the two instinctively hide in the closet. Surprisingly, this roommate is Kaede’s direct superior! ?Kaede's heart pounds as they press against each other in an attempt not to be noticed and Shioya's lips touch Kaede's chest. Kaede is overjoyed when the turn of events bringing her closer to Shioya, whom she secretly admires. Shioya looks at her with cool but kind eyes. Then Mizoguchi his roommate gets involved, marking the beginning of a love triangle.?