1. Combine sugar and lime juice in a pan. Stir in 1/2 cup cold water and bring to a boil over high heat, stirring until sugar dissolves and mixture thickens slightly. Remove from heat and let cool, 10 minutes.
2. In a large bowl, combine mangoes, pineapple, lychees and orange sections. Pour lime syrup over fruit and gently stir. Chill for at least 1 hour. Just before serving, fold in bananas.