Quote Originally Posted by Loony BoB View Post
Oh, she's definitely cold. Coldness isn't just from the deep internal feels. It's also how you present yourself. And the way that Lightning presents herself to people she's not met before is what I would describe as cold.

I'm pretty sure both characters are described as cold in their respective games at some point.
It's not about internal feelings, it's about context. Under normal circumstances maybe you'd be right, however since Lightning is introduced while life-risking events are taking place, things are a lot different.
First of all she was being targeted by the Sanctum's army, which was trying to purge the citizens of Bodhum, so she was already fighting with her life on the line. More importantly she was rushing to the Vestige to save Serah, she literally couldn't waste a second of her time (and we know how important Serah is to her). Plus Light was already very angry at that time, and for very good reasons.
Also let's not forget that Sazh wasn't helping her at all. He was just following her around to avoid getting killed. Anyone would get pissed in that situation, not just Lightning.

Overall she does appear to be cold, but that's just until the moment you realize what was actually going on, until you're given context to those events.