Light Yagami gains control over Misa Amane by using the Death Note to manipulate her memories and emotions. He first makes her fall in love with him by having her trade half of her remaining lifespan for the Shinigami Eyes, which allows her to see others' names and lifespans just by looking at them. This deepens her loyalty and devotion to Light, making her willing to do anything he asks in order to help him achieve his goals.
