Kasi is the remake of Malayalam movie VaVasanthiyum Lakshmiyum Pinne Njaanum. Kasi (Vikram), makes a living by singing by the roadside and village fairs. Kasi belongs to a household of a bedridden dad (Vinu Chakravathy) who has a sharp tongue, a drunk brother ( Thalaivasal), a mom (Vadivukarasi) and a doting sister Lakshmi who thinks the world of her brother. Kasi falls in love with his sisters friend Kaveri (Kaveri) who is a mute girl. Rajiv is a ex-MP who comes back for a holiday with his friends. Rajiv is worshiped by the village people. Kasi holds Rajiv near and dear to his heart like the others.
Rajiv with a help of a US returned doctor is going to attempt to fix Kasi’s eyes. Kaveri and Lakshmi pay a visit to Rajiv. The unthinkable happens. Both girls are rapped. The girls keep quiet about the rape in fear they will Rajiv will not help Kasi to regain his eyesight. Rajiv calls upon Lakshmi to discuss the operation. Instead of a dicussion Rajiv rapes Lakshmi again and rewards her with cash. Lakshmi feels like a prostitute and commits suicide. Kasi finds out of his sisters rape and takes revenge.