Harukana Chi No Yakusoku / Original Title: MARRYING the ROYAL MARINE (mirabooks)

[Machine Translation] As the illegitimate daughter of a viscount, Polly was confined to a girls' school until she turned 18. When she boarded a ship to visit her sister in another country, it was the first time she had ever known the outside world. Surrounded by rough men and full of insecurities, Polly is given a helping hand by Lieutenant Colonel Hugh of the Marine Corps. Polly is attracted to him, but he is 19 years older than her, an elite officer, and she is nothing more than an ugly duckling who longs to be with her beautiful sisters....

子爵の非嫡出子として、18歳になるまで女学校に閉じ込められていたポリー。そんな彼女にとって、異国の姉を訪ねるため乗った船上での日々は初めて知る外の世界だった。荒くれ男に囲まれ不安だらけの箱入り娘に手を差し伸べたのは、海兵隊の中佐ヒュー。ハンサムで紳士的な彼にポリーは惹かれていくが、相手は19も年上のエリート将校、自分は美しい姉達に憧れる醜いアヒルの子でしかなく...。