Rubina has vast power and can summon endless shadow soldiers to fight for her. She can control them with ease.
While not showing much emotion, Rubina truly enjoy fighting strong opponent and the thought of chance to fight with the other Trinity Seven, such as Levi who managed to injure her, excites her.
Rubina's nature as Demon is becoming one with the concept of Darkness. With this she can get endless power from darkness. Rubina's attack also deals physical and mental damage, and could possibly destroy Albalisha whose nature is living as her host's mind (according to Albalisha).
Also because of her nature, even after she got consumed by Graffia with power of the True Demon King, and her magic power disappeared, she could still return because she is darkness itself (according to Libik).
Road of Nightmare - Rubina summons a hollow grim reaper which she controls using threads connected to her fingers. She is capable of summoning many of them to take down stronger enemies as well.