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To be honest, if it weren't for the RPG element, I would have considered Darkness or Water. Immunity to negative effects and injuries, regeneration, and stunning on attacks look incredibly appealing. Perhaps Light, due to its low cost and renewable companions. Alaria would assemble her own harem, without gambling or trading situations. But it would be strange for her to choose anything other than Fire, even though it's not the most optimal option. Of course, one could try to justify something with meridians, but that's just a thought. Unless I came here without losing all my skills, then there would be a point in choosing Darkness.
Added after 26 minutes
I could, by the way, earn 1500 rems a month as a waitress if I chose Light...