The Scarlet Moon

No matter how worried he was about what happened to Natasha, he was unable to help her in the situation right now—Lucien was very well aware of this fact. Therefore, he managed to put all the thoughts behind and focused on what he was faced with right now.

With the castle's magic circles resisting the imposing pressure from the Legendary, Lucien was sheltered and could thus still stay focused. He looked up, and when he saw a remaining thin layer of the silver moon's light, his soul felt the special connection again.

Lucien quickly drew his conclusion: Although the moon was blocked, the remaining light was still able to provide power to the summoning magic circle, and the level of the magic circle was close to the power of Dracula! Also, it seemed that the summoning magic circle had a bit to do with Alterna, as She had left Her imprint on it!