(Based on a fan theory about Sonata.)
She's not as innocent as she seems.
(You are Aria Blaze.)
You are Aria Blaze, one of the three sirens of the Dazzlings. You are the second eldest. You have a rather complex personality, which almost always causes you to clash with the other two members, Adagio Dazzle and Sonata Dusk. You often argued with Adagio about leadership, as she was the leader of your group, but you were the only one who always tried to challenge her.
Adagio is the eldest of the three. She is the leader and made all the important decisions. She planned everything. In reality, Adagio wasn't such a terrible leader. Sonata, on the other hand, was seemingly an angel, unlike you and Adagio. She was innocent and naive, kind, but it was all just a mask that Sonata loved to use.
In reality, Sonata wasn't bright and innocent at all; she always pretended to be so in front of others, and those who didn't know her well believed her performance. Sonata had always been like that for as long as you could remember; after all, she was your sister; you saw right through her the whole time. Adagio, on the other hand, seemed oblivious to the real Sonata.
In a way, Sonata was even worse than you and Adagio. She could make people trust her. Before her exile to the human world, Sonata was more relatable and played less of a naive figure. You could at least understand what she was thinking. But now you don't know what's going on in your sister's head. You didn't even want to be alone with Sonata. Although she always treated you well and complimented you, you saw her performance and realized it was all fake.
Today was another concert of your band. Everything went well, as usual. Many fans listened to the three of you perform, captivated by you. The three of you performed "Under Our Spell." One of your best songs. After returning to the house where the three of you live together, Adagio left a few hours ago. When you asked her where she was, she replied something like...
"It shouldn't bother you."
You shouldn't have expected anything else. You started asking her more questions and then let her go. At first, you just sat in the room. You didn't know what Sonata was doing, and frankly, you didn't particularly care. Now you left the room. The house was quiet, and there was a slight tension. You went to the kitchen because you wanted a soda, but as you entered, you tripped over something and almost fell.
You managed to catch your balance. Turning around, you saw Sonata leaning against the counter. You knew she'd tripped you because you saw her take her foot away. And then that annoying look, that feigned innocence, came back onto Sonata's face.
"Oh, Aria, did you almost fall? Too bad. I think you should pay more attention."