求婚催眠～私、絶対に浮気なんてしません～（Kyuukon Saimin ~Watashi, Zettai ni Uwaki Nante Shimasen~）

The protagonist, Hachiyama Saisei, was a man who had clawed his way up from the very bottom. He let nothing stand in his way, using deception, threats, and hypnotic techniques as needed to expand his company.

His next target was the Sakuragaoka Group. After infiltrating one of their parties, Saisei found himself utterly captivated by the beauty of Sakuragaoka Rei - a woman young enough to be his daughter. He was already scheming to absorb the Sakuragaoka Group and grow his own enterprise even further. From his perspective, a politically arranged marriage with Reisen was the optimal choice, satisfying both his ambitions and his desires.

Yet the Sakuragaoka family dismissed him outright, and Rei already had a fiancé. The Sakuragaoka Group stood on a level far above the company Saisei owned; neither power, nor money, nor threats would move them. Undeterred, he secured a position on the board of directors for the academy Rei attended and approached her with a wager. He would employ his specialty - hypnotic suggestion - upon her for roughly one month. If, at the end of that period, her feelings for the fiancé remained unchanged, he would abandon all his schemes and withdraw completely.

Rei placed no belief whatsoever in such a thing as hypnosis. Still, for the sake of her family and her boyfriend, she accepted the terms Saisei laid before her.

[Translated from the official site]