Mother remarried, two daughters were raped by stepfather

Yui and Mitsuki are two siblings with the same father but different mothers. Their mother is very poor, and their father still has to pay off a debt left by him. One day, their mother said she would remarry, even though the man is quite old, he can pay off the debt for them. Despite feeling skeptical, when they saw their mother's long-lost happy smile, they agreed.

And then they were able to live the wealthy life they had always dreamed of. But after a while, they realized the true nature of their stepfather. Whenever their mother wasn't around, he would continuously harass the two siblings and threaten to kick all three of them out if they dared to reveal this...