Rantaro is a laid-back and calm man who has the title of Ultimate Adventurer and Ultimate Survivor. He has green hair and eyes. He wears a baggy, striped shirt with a necklace with a bullet of sorts. He has 1 biological and 11 stepsisters, who are all lost around the world. Rantaro shows a deep feeling of survivor's guilt, but he hides it behind a gentle smile. Shuichi, the ultimate detective, noted how he only truly smiled after he promised to help Rantaro find his siblings.