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Mom yelled up the stairs. "Light, Sayu, Shisuta! Dinnertime!"
Light was the first to arrive, and Sayu saw him walk neatly down the stairs before her, but he often was, ever the dutiful son.
Shisuta was already downstairs when Sayu arrived. "Who are you?" Sayu asked her, fearful. Shisuta just looked at her, eyes confused, but it was Light that responded.
"Sayu, she's our sister. Are you feeling alright?"
"We don't have a sister, Light." Sayu explained in the tone of a person who knows they are right but is arguing with a kindergartner.
"Sayu, you're scaring me. Shisuta is your sister." Mom said, and that was that.
Light reached to bring the big pot of sukiyaki to the table, so Sayu made for the plates, as she normally did. But the stranger, her sister had already grabbed them, so she reached for the utensils, disconcerted. Then they all sat down, but Sayu's seat was shifted, the usual (it had to be usual, right?) dynamic was off, now with Sayu seated next to Shisuta and Mom, so that Light was across from her. None of the others seemed at all distressed- in fact, Shisuta was cheery, whistling a bit as she grabbed at the food.
"Yum, Mom, looks delicious!" Shisuta remarked."
"Yes, thank you, Mom." Light said, smiling at her.
Mom smiled at them. "Thank you, children."
Light seemed fine with Shisuta. Mom seemed fine with Shisuta. Shisuta, of course, was fine with Shisuta. So why did Sayu feel so wrong about her?
The air filled with the sounds of chewing. A few swallows, here and there, but mainly a blanket of silence.
Sayu reached for an easy conversational topic, anything to breech the tension that gripped her and only her.
"Light, do you know how's the Kira investigation going?"
Light's brow wrinkled, somehow eloquent. "The what? Oh, has one of the cases I help with been given a nickname by one of your shows?"
Shisuta laughed gently. "Or maybe she's confused one of her shows with the real world."
Sayu scowled. "I have no idea what you're talking about! Dad's out because he's on the Task Force, remember? The Task Force for the Kira investigation. That was all over the news."
Mom's face twisted to one of concern. "Sayu, your father isn't here because his work as the Chief of Police keeps him very busy. Not this 'Kira investigation'. First asking who Shisuta was, now this. Are you feeling okay?"
Sayu stood up. "No, because this stranger broke into our house and has convinced you she's your daughter!"
Shisuta stood up, suddenly, and ran past Sayu upstairs. Light glanced at Mom, then followed after her, the picture of concern.
"Sayu. This isn't funny." Mom said sternly.
"I don't think it is! Are you feeling alright? Because it seems like all of you are the crazy people. Why do none of our pictures have Shisuta, then, if she's supposed to be my sister?" Sayu reached around for a picture, the one on the mantle, of her and Light on a roller coaster.
She spun it around, triumphant, but stopped, catching a glimpse. A perfectly generic girl sat in Sayu's place: long, black hair, a round face, almost as perfect as Light but more symmetrical. The girl looked like what Shisuta had: the idea of a 'Girl', or a 'Sister'.
"Sayu. That's Shisuta, right there. She was born a few years after you, remember? Oh, I'm going to call someone." Mom got up and paced. Dinner lay forgotten between them.
Sayu took a breath, and decided. "Mom, you don't need to call anyone. I just got a little confused, that's all. I promise. I'll go apologize to Shisuta."
Mom nodded, a bit wary. "Alright, then. I'll cover dinner with something warm."
Sayu walked up the stairs, resolving herself. She knocked on the door to the guest bedroom. Shisuta's bedroom.
"Shisuta? Can I come in?"
Shisuta, sniffling, said yes. So Sayu opened the door, and sat cross-legged, staring at the preteen in front of her who was clutching her knees.
She looked like an ordinary child. She looked like Sayu's sister.
She couldn't possibly be. Magic was real. It had to be, after all, if Kira was going around killing people like that, and a truth of Sayu's life was that there was a Kira who wanted to kill her father. That couldn't be a lie.
Sayu leaned forwards, grabbing Shisuta's shoulders, and whispering into her snot-stained hair. "I know you aren't my sister, and I'm going to prove it."
Shisuta looked at her, dull and numb. Then something about her changed, and she no longer looked like the terrified child she had a moment again, though nothing about her appearance changed in any way. It was a presence that wasn't there. It was an absence.
"Yagami Sayu, I could get rid of you so easily." It was delivered in the tone of a secret. It was delivered in the tone of an absolute truth, and Sayu became so deeply certain of it, more than her own name.
Then Yagami Shisuta leaned back, and resumed sobbing. Light walked in, hugging her sideways. Sideways hugs were always reserved for Sayu. Not so anymore, apparently. No more conversation, real conversation, would be had with Light in the room.
"Sayu, you can't keep accusing Shisuta of not existing." Light said calmly.
"Or what?" Sayu challenged. "She'll make me not exist? Nice try."
Shisuta was still crying, but she looked up, eyes streaming tears, to stare at Sayu.
Light blinked. "Don't be ridiculous. She's obviously not going to kill you."
"I wouldn't be so sure," Sayu muttered, but Light either didn't hear it or didn't care.
"Mom and I will take you to the psychiatrist. This isn't a threat or a punishment, but it seems like you're clearly in a delusional and paranoid state. I have an obligation to both you and Shisuta, and it's best for both of you if you get the help you need, Sayu."
Now it was Sayu's turn to blink. "What I need is for her to be gone! Or failing that, for her to explain what she wants."
Light took Shisuta's hand, and squeezed it to comfort Shisuta as she spoke. "Sister, all I want is for us to be a happy family. That's the truth." And that same paralyzing absence of a person was back, strong, before it abated.
"Maybe you should get some rest. You might feel better in the morning." Light advised Sayu. So Sayu headed to her room and left that unfathomable lack of a person alone with her brother. It was the strangest thing, though. Sayu didn't feel like Shisuta would harm him. That would be rather contrary to the point of a happy family, after all.
Her dreams were strange. Before her was a scale. A pulsing human heart, staked through with a pen, lay on one side, and the other was covered with a cloth sheet. All around were scales, each balancing up and down. A small notebook, which Sayu flipped through, balanced on another stool. It was full of names and graphic descriptions of deaths. The other side was, again, covered by a cloth sheet.
She wandered and wandering, and before her came the Being, and it deigned to speak to her.
"Yagami Sayu, why do you resist this so?"
"I'm sorry?" Sayu said, politely.
"Your brother had no problems accepting this reality."
"What do you mean, 'this reality'?" Sayu spoke to the ember-carrying eye, and it deigned to reply.
"You are correct, in that there was no Shisuta Yagami born after you. But there is now. I was not in the first world, and I am in this one. That is all that is different."
"I don't believe you," said Sayu, sing-song.
"What do you not believe, other than that there is a world where you can be happy?"
"You expect me to believe that all you want is for me to be happy?" Sayu demanded of the sworld-wielder, and it deigned to reply.
"I was not of the family Yagami, and now I am. Reality just adjusted to match what is true. Is it so hard to believe that I wish my family to be happy?"
"Why me and Mom and Light?" Sayu offered, to Yagami Shisuta.
"Your world before was truly terrible to you. Your world with me is not. Now you, Yagami Sayu, have a choice to make."
"What is this choice?" Sayu knelt down, supplicant. Yagami Shisuta knelt down besides her, so their hands just barely touched.
The scales all fell above them, tense as a violin string.
"Yagami Sayu, you can live in the world before me, where you would be kidnapped, and your father killed at your brother's hand, and your mother swallowed by grief, and your brother dead in a warehouse in a pool of blood. Or you can live in this world, where we can all be a family." said Shisuta.
Sayu closed her eyes, on the precipice of a needle. Then she fell, and the world she had chosen slotted into place.
Sayu woke up, and headed downstairs to help Mom with breakfast.