反抗的なヤンキー少女（クラスメート）との絶対主従関係（Hankouteki na Yankee Shoujo (Classmate) to no Zettai Shujuu Kankei）

Kouta was born as the heir of a large pharmaceutical company that invested heavily in his school.

He has always been able to get whatever he wanted, but there was only one person he could not get yet.

It is a Yankee girl named “Asuna,” who is determined to be a lone heroine.

Kota, who has tried everything to get her but has been defeated, and has never been able to get close to her, is faced with a turning point.

Through the tears of the Yankee girl, he learns of the existence of her younger brother, who suffers from an incurable disease, and the existence of a medicine that can cure his illness.
Asuna quits school and sells herself to get medicine for her brother.
Asuna ends up in the hands of a man she doesn't know.
Kouta does not choose the means, nor does he care about the means.

Kouta, using the power of his birth and his family's pharmaceutical company, demands Asuna's life in exchange for the medicine.

He plots to get his hands on Asuna.

Asuna, who is ready to give up everything for her brother, accepts Kota's demand and makes a contract with him.

[Translated from DL site]