Hakushaku to Yousei ~Yume to Kizuna ni Omoi o Hasete~

The story, set in Victorian England, follows the adventures of 17-year old Lydia Carlton, nicknamed the "Fairy Doctor" due to her interest and understanding of fairies. Her life takes a 180-degree turn when she meets Edgar J.C Ashenbert, the "Legendary Blue Knight Count" and his crew on a sea voyage to London. Edgar hires her as an advisor during his quest to obtain a treasured sword that was supposed to be handed down to him by his family.

[From Wikipedia]