I'm sure that kind of thing is possible, but you wouldn't describe said person as "friendly, bubbly, kind and caring", right? The character I'm describing is not one with deep seated psychological issues, its an apparently "normal" or "nice" person that turns into a LETHAL KILLING MACHINE™ when they enter combat, and they don't pay much attention to the act of killing when they have to do it. I mean, sure, maybe someone would hide their true nature by pretending to be everyone's best friend, but the characters I'm describing are portrayed as perfectly normal yet capable of killing without batting an eye.