Seeing as he doesn't remember his talent at the beginning of the Killing Game, he is the Ultimate ???. Rantaro is a carefree and relaxed person, and he is described as one of the more ordinary students despite his mysteriousness, with he stating that he can sometimes get a bit overwhelmed by the others' stranger personalities. Nevertheless, he is shown to have more patience than others with some eccentric students like Kokichi Oma and Miu Iruma, tending to just laugh off some of the potentially hurtful things they say. Even though Rantaro cannot remember his talent, he doesn't seem worried about it, instead, he simply says he just looks forward to finding out what it is. Despite his appearance and manner of speech, he has cold, excellent insight, and is both determined and brave. He even has downright frightening expressions whenever he gets very serious. People (especially girls) occasionally seem to assume that Rantaro is a womanizer, he is aware that he looks like a "playboy", but he always insists he isn't that kind of person and he doesn't have a girlfriend, stating that he's just a chill, friendly guy. Instead, due to having multiple little sisters, he acts like a responsible big brother toward some of his classmates. He has great knowledge of concepts that are considered feminine because he used to help his younger sisters with certain things like schoolwork and nail art. Rantaro is shown to be a bit unsure of himself. A lot of this anxiety is related to the stress caused by his sisters' situation, but he is also shown to be a bit insecure about his memory issues, assuming that others wouldn't trust someone like him and wondering if he can even trust himself.