Ore no "Unmei no Akai Ito" ni Tsunagatteta no wa, Tenteki no youna Joshi datta Ken

On April 22nd, in the year you turn 16 years old, a red thread will appear on the ring finger of your left hand. It is said that the thread is connected to your soul-mate somewhere in the world, and that if you are united with that person, you will surely be happy. Akito Sanada's red thread is connected to his classmate, Riran Kuonji, with whom he constantly fights whenever they see each other. The relationship between the two don't seem improved even though they are connected by the red thread, as they both believe that they are hated by each other. A sweet but trying love story between a clumsy beauty and a slightly insensitive boy. (Source: Fantasia Bunko, translated)