Ferdinand is the head priest in the temple of Ehrenfest, as well as the patron and educator of Myne in the temple. Ferdinand teaches and guides her to be a 'proper' shrine maiden and noble lady.

He joined the temple on the suggestion of his older brother to avoid noble politics. Despite being the second in rank in the temple, most of the day to day administration is handled by him.

Ferdinand is described as a sharp-minded, calm, and dignified individual, so he comes across as a lot older than he really is, leading many people to be surprised by his real age. He has a bit of a fussy personality, leading him to take on all sorts of responsibilities, including Myne's education. Ferdinand is meritocratic in spite of his social status, despising incompetence and laziness the most, and earning him the reputation of a harsh disciplinarian who would cut off anyone who couldn't meet his standard. The same trait leads him to favor Myne ever since their first interaction, calling her worthwhile to educate.

Due to his harsh past, Ferdinand tends to be secretive and distant even to his companions. He is also poor at showing emotions, and interacting with Myne helps him to be more expressive and human.

(Source: Ascendance of a Bookworm Wiki)