快感戦士バスティー

Main heroine enters a private high school.
One day her best friend gets attacked at the school roof by some boys, so heroine stands up to protect her. At that time heroine is transformed into a busty pink warrior by space police. It turns out that members of evil organization hunt for big bust girls as their perverted energy spreads this way with the ultimate aim of creating a country of perversity. Protagonist needs to find the lair of trouble while fighting organization members.

[From vndbreview]