Character design is usually misunderstood as a job limited to character artists or scenario writers. That's not true anymore in next generation open world games, where players spend 99% of the time playing and not watching cutscenes. For this reason, game designers at Square Enix now focus on character storytelling by AI, and how to actualize them for the player, instead of only setting the characters. However, the concept of character storytelling by AI is still new and challenging. Game design, AI architecture design, and emotional experience design call for different expertise, but are all needed to create a living, experience-engaging AI-buddy, especially in a big and complicated open world game such as 'Final Fantasy XV'. In this talk speaker Prasert "Sun" Prasertvithyakarn will share with how he and his team at Square Enix combined these three designs to bring their three AI-buddies Prompto, Gladiolus and Ignis to life, pioneering the field, and searching for new approaches for the next generation to come.