Kamen Hakushaku wa Kurosuishou no Hanayome ni Koi wo Suru

Christa was sold off by her scheming stepmother in an arranged marriage to Lord Gerald, a notorious misanthrope who always wears a mask. Gerald tells Christa coldly, "It is not a wife I need, but an heir." But Gerald is actually hiding a secret that he cannot tell anyone...?
(Source: FK Comics, translated)