Like Iron Tail is to Evil Tail, Sehsa Nightmare is the opposite to her sister, Ashes. Both are blessed with physical beauty, but only Sehsa exploits it to no end, using it to seduce people to get things she wants. While Ashes is more honorable and respectful, Sehsa would not think twice about playing dirty and insulting those around her. The only person she's loyal to is Evil Tail, who she treats with the utmost respect, even calling him 'Master'.
Her goal is simple: chaos. Believing that the current world is wrong and dull, she wishes to plunge the world into darkness, where the strong rule and the weak dies - a world promised to her by Evil Tail.
Like her sister, she's also one of the more tragic characters, but for a different reason.