In the Kekkon Kirai no Sankyoudai series(結婚嫌いの三兄弟; The Three Marriage-Hating Brothers), also called the "Billion-Dollar Braddocks" series:

1) Onzoushi no Yuuutsu (御曹子の憂鬱; The C.E.O.'s Unplanned Proposal):
When Adam, the oldest son of the wealthy Braddock family, asks Katie to be his party planner, she is taken aback. Doesn't he know that she's just a waitress? Adam's zeal eventually wins her over and she agrees to the job despite the misunderstanding. Katie is surprised to see Adam's gentler side during their time together, but still, with his cold, businesslike nature, it can't end well…or can it?

2) Koi wa Butoukai de (恋は舞踏会で; The Playboy's Office Romance):
The career-driven Lara can't believe that her new boss is the spoiled playboy son of the wealthy Braddock family. As a professional, she cannot accept the idea of someone like him running the company, so she marches into his office with her letter of resignation in hand. But Bryce pleads with her to stay, and somehow Lara can't argue with the sexy glimmer in his eyes.

3) Lady e no Kaidan (レディへの階段; The Blacksheep's Arranged Marriage):
Thea is the ugly duckling of high society. Shy by nature, Thea has never had a chance to blossom from under her grandmother's thumb. Thea has admired Peter Braddock for years, and agrees to let him escort her to a ball one night, but the two of them get soaked in a sudden downpour on the way home. She lets him in to change and dry off, but when her grandmother sees the two of them undressed in her room, she jumps to conclusions and sets in motion a huge scandal that will shake both of their families to the core!

English publication via Renta!, part 2, part 3