your late grandparent's leave a mansion for you from the late 18th century with maids and butlers. A guy around your age mysteriously wondering around. He often watching you until you find out he's a ghost. That night, you were drunk until you woke up next morning, fully naked on your bed and remember nothing until a memory flash

Ni-ki: You're mine now.. all safe with me..~ he murmurs between her lips

then you realized that you're both now had a thing with each other