堕姫

The main character's father is the boss of his tribe, living in "Shadow". He does nothing and just lives lazily. One day, his village is attacked by another tribe but he hides himself in his secret base and still fools around with girls. But he is found and almost killed, and thrown away in a river..... Just before he dies, he is saved by a man. His job is to train girls to sell them as sex slave but he is kind and takes a good care of him. When he recovers, he kills the man and gets his energy, knowledge and skills. Also, he gets the man's tattoo to prove he belongs to the tribe and new face. He doesn't go back to his homeland, just traipses around the human world. One night, he receives an offer to train three girls for seven days. He accepts his offer and his training starts...