18+ Mitsuya no Bara ni Kuchizuke wo

Holly Colette has snuck into the Granville Castle, but not maliciously. Quite the contrary, Holly Colette has snuck into the Granville Castle because she wants to hand-deliver a letter to the man who saved her life. Holly spent a part of her childhood in the castle but has not been back since she left for school ten years earlier. Her memory is hazy, but... oh yes! This must be his room! While waiting, Holly dozes off and... wakes up to her rescuer mistaking her for his bride!? Holly is about to learn the truth about the old castle and her savior, the mysterious Gideon Granville!

(Source: Fantasista Inc.)