So far the story is meh. I liked Prism, so I expected something more. We're still in the begging though so who knows.
It's basically a cute girls who happen to also be vampire story. You know, when them being a vampire is just for extra points instead of having a plot around it.
Also I don't understand why she didn't just brainwash someone else to kill her instead, if she wanted to die. Feels more like a plot hole
She started to explain that there was an additional requirement for the sword to kill her. Probably something about Ichika's bloodline, since she implied something about her grandmother and the sword right before Ichika confessed her love to Aria. It might also require her to be a virgin, which would mean that she's the only living person capable of killing her with it. Or it might require that she love her, but Aria didn't know that yet, so it's probably not that.