A person with fire related powers is calm and collected instead of hot headed.
Fire is energetic, so making people with fire related powers passionate is almost an effective form of shorthand as giving them red hair or clothes. On the other hand, there's this trope. Giving fire users (or Mad Bombers and Grenadiers) a more stoic or calm personality contrasts nicely with their abilities. It's often justified In-Universe by explaining that they need to be calm and composed to control their chosen element. While it might seem like a complete inversion of the "usual" personality type associated with fire users, they also have a less restrained or outright sadistic personality (which might be their "true self" or might even be closer to a Super-Powered Evil Side) which slips through sometimes (in which case, expect plenty of "burning out of control" metaphors). Despite being at odds to more passionate portrayals of fire users, this can still be considered a Personality Power; the calm personality can represent the hearth and hospitality or industry which fire is symbolically associated with (and a darker, hidden personality can represent the threat fire can still pose). Compare Genius Bruiser (for another character archetype which contrasts with their usual portrayal) and An Ice Person (who this personality is normally associated with). Contrast Mad Bomber and Pyromaniac.
Examples:Anime and Manga