Biko can be described as a "stalking simulation". You play as Akira, a guy who stalks pretty girls. When you make your choice from the five available girls, you have to stalk and pursue them through various city locals.
After you successfully pursue the girl through several areas you finally run her down and are presented with a number of CG images, animation and eventually an interactive 3D rape scene. But the ending depends on the choices that you made in the beginning - you may get a romantic ending, sadistic ending, or the girl might just run away.