Taisho era. Main character comes from a Chinese family. With his mother dead and father travel around the world. protagonist spends most of his time together with the girl Yui picked up and adopted to the family at a young age. One day siblings find a chest at the mansion and open it, but there is nothing inside. The same night after incredible light splash Yui's eyes turn red and hair blonde. Protagonist loses consciousness because of blood being sucked from his neck. But he wakes up from the tremendous pleasures body receives.

[From vndbreview]