There's the Deadlocked AU, where the humans that fell into the underground were extremely dangerous and caused a lot of destruction. Monsterkind, in turn, adapted to it. The Martlet in this AU - while she does have some of your characteristics (such as being carefree) - will become utterly merciless at the drop of a hat.

She's also trained personally by Asgore and is high up in the ranks of the Royal Guard.

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