Rantaro Amami is the Ultimate Adventurer and the main protagonist of the story. "He's largely a carefree and relaxed person, and he is actually  one of the more ordinary students in the cast, with he himself stating that he can sometimes get a bit overwhelmed by the others' stranger personalities. 

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."  (Source) 

In the end, he despises Monokuma and is willing to stop the killing game, whatever it takes.

For Rantaro, I'm looking for someone who can mimic his voice from the official game very well (here are his voice clips to give you an idea of what he sounds like: https://youtu.be/8Nfh9beKX6k)