Watch The Last Birthday (2025) : Full Movie Online Free A large family gather to celebrate a birthday. It would seem like a great reason to get together. But the family is just a project of one of the "brothers" — an experienced psychologist who is conducting an experiment to create a "happiness formula". He believes that manipulating others, their emotions and desires, will make them happy. However, love interferes with the mathematical calculations, which can neither be calculated nor predicted.