As one would expect from the Shield Hero. Naofumi Iwatani is distrusting and cynical until learning to open up, sees his role as a hero to be a burden, and being willing to use underhanded tactics to ensure the survival of him and his party. 

He's also taken a liking to being inflated in several ways, with his most preferred way being to inflate himself. He's also good at masking any enjoyment during inopportune times like during battle. He also likes to inflate alongside his love Raphtalia.