Chapter 3
My little sister, Yu Arin, was born.
Seolae was busy cradling Arin and soothing her, while Jinhu rummaged through the drawers beside her, looking for things like diapers and moisturizer.
Now that I could walk freely, I looked at Arin lying in the crib.
So tiny.
She could barely open her eyes, and her cries were abnormally loud for her lung capacity.
Was I like that 20 months ago too?
‘Good. Now I should be able to move around a little more freely.’
A realistic thought followed.
From now on, Seolae and Jinhu's supervision would become significantly looser.
Up until now, I'd been a good child who had never put toys in my mouth or dropped anything.
I had stayed a quiet kid who didn't cause any major trouble, so Seolae and Jinhu would relax and pour their energy into taking care of Arin.
‘I'll slip into the study and get the research materials while I have the chance.’
At first, that's what I thought.
Or rather, that's what I wanted to think.
But then...
“Waaah!”
As soon as Arin burst into tears, Seolae smiled despite her tired face and soothed her.
“It's okay, Arin. Mommy's here.”
Jinhu, beside her, was busy preparing things for Arin.
Watching that scene, a memory suddenly surfaced.
-Becoming a mother is as valuable as doing math, if not more so.
Right.
I said that myself.
When Seolae chose childcare over research, I told her it wasn't the wrong choice, and I even encouraged her decision.
But.
‘...What am I thinking right now?’
The first thought I had on Arin's first night home in this world was, 'The supervision will be looser.'
A new family member had been added.
My little sister had been born.
Mom and Dad were so happy, and so tired.
And I was thinking about my paper.
‘...After saying that with my own mouth.’
After saying that building a family was more valuable than doing math.
Yet I, the one who said it, understood it least of all.
“S-sorry...”
I closed my eyes soundlessly and reflected quietly.
Even if I didn't rush, the Riemann Hypothesis was a problem no one had solved for 160 years.
‘So, I guess it’s fine if I wait a little longer...’
Obsessing over the paper to the point of neglecting my family was just my own desire.
I remembered that in my previous life, Jinhu had once given me a talking-to because I was obsessed with results.
Now that I'd been reborn, maybe I should change my attitude toward life a little.
✒️✒️✒️
After Arin was born, I changed a little.
I hadn't given up on writing the paper.
It had just slipped a little in priority.
Anyway, it was a long-term project that would take years.
And I decided to accept my identity not as Shin Ijun's reincarnation, but simply as Yu Ayeon, a girl carrying the memories of Professor Shin Ijun's former life.
I'd been hesitating for a while, but it seemed the trigger really had fully kicked in once I got a little sister.
Because Shin Ijun died of a heart attack that day.
Now I was just my mom and dad's beloved daughter.
When Mom had put Arin to sleep and was slumped on the sofa, staring blankly, I quietly walked over and sat beside her.
“Ayeon?”
“Yeah.”
I gently rested my head against her.
I didn't throw a tantrum because I felt sorry for Mom.
I'm a good child who doesn't throw tantrums.
Mom looked down at me for a moment, then patted my head.
Pat-pat-.
“Our Ayeon is such a good girl.”
“Nihihi.”
When family members who love each other make contact, a hormone called oxytocin is released.
And between 12 and 36 months of age, the limbic system develops and becomes very sensitive to hormone release.
So... being patted by Mom and feeling warmth in my chest and happiness is a very natural response.
That definitely doesn't mean something is wrong with me...!
‘It's a waste for only me to enjoy this wonderful oxytocin.’
Whenever Arin burst into tears, I would go over to her side and gently hold her hand.
Strangely enough, whenever I held her hand, Arin would stop crying immediately.
“Ayeon really looks after her little sister. You're a proper big sister now.”
Dad looked at the scene with a pleased smile.
Big sister.
That word echoed strangely in my heart.
‘Yeah. I'm the big sister. A big sister who sets a good example for Arin.’
Hehe.
Before I knew it, the corners of my mouth lifted.
✒️✒️✒️
24 months old. Two years old.
The stage where you pass infancy and enter toddlerhood.
I'd already finished all the annoying baby milestones.
Now I wore pants instead of diapers, no longer nursed, didn't use a pacifier, didn't burst into tears all the time, and above all, I could walk steadily on my own.
My mouth still wasn't developed enough to speak fluently, but even so, I could communicate well enough with Mom and Dad.
However, I didn't want to get caught going into the study to look at research notes and write a paper, so I had vaguely waited until I was big enough to quietly open the study door on my own.
And finally, the chance came.
The time when the three of us—Mom, Arin, and me—took a nap together.
I'd stocked up on energy by sleeping a lot the day before.
Flash!
As I opened my eyes, I slipped out of Mom's arms.
And then I tiptoed toward the study.
“Hngh-.”
My hands barely reached the doorknob, even when I stood on tiptoe and stretched my arms high.
I had done stretching exercises every spare moment just to reach this doorknob.
Click-.
At last, the study door opened.
‘I'm here...!’
I quietly opened the door so I wouldn't wake Mom and slipped into the study.
Rows of bookshelves packed with books, the smell unique to wooden furniture, and boxes stacked in the corner.
I slowly started looking for the materials.
I swept through the materials on the lower shelves, and it seemed the lower shelves held the materials Mom had studied back when she was in her master's program.
‘This is the book I recommended ages ago because I liked it. Oh, this too. She bought the hardcover? That's pretty expensive.’
Okay. No luck on the lower shelves.
I lifted my gaze.
“N-no, it's too high...”
But I was a child who didn't know how to give up.
I immediately pushed the study chair with both hands and climbed onto it with my whole body.
“Hyaaah!”
Climbing onto an adult chair in a child's body wasn't easy, but I managed to get up with all my strength.
My ten-thousand-times-a-day gratitude wiggles and visualization training had paid off.
After fully engaging my semicircular canals to keep my balance, I reached for the upper shelf and managed to get hold of a clear file.
[Professor Shin Ijun's research materials—Research on the Riemann Hypothesis? Order unknown]
A file organized in Mom's handwriting.
Swish-.
When I opened the file, I could confirm that it contained messy formulas written in my own handwriting from my previous life.
ζ(s) = Π(p: prime) 1/(1 - p^(-s))
Seeing the familiar expansion of the Riemann zeta function, I was certain this was the research notebook I had agonized over for three months in seclusion.
“This is it...!”
But my joy at finding the research notes lasted only a moment before I ran into another problem.
“Uh...? Why can't I read this...?”
The problem was that the handwriting was so atrocious I couldn't decipher it!
Did I really write with this sort of handwriting in my previous life?
Even two years and ten months after my death, seeing it again in a child's body, it was truly horrendous chicken-scratch.
“If I had a dance battle with an earthworm, I'd probably win...”
Suddenly, I remembered something I'd overheard Mom say when I was a newborn.
-Since no one could decipher it, I ended up taking it over as the only disciple.
Because the handwriting was so bad that no one could decipher it, Mom—rather than another professor—was the one who inherited the materials, and thanks to that, I could read this notebook now.
Should I be happy about that or not...
‘Anyway, if I take the time to read it, the memories will come back slowly. I have plenty of time.’
Thinking that, I secretly tucked the clean copy of the research notes into the lower shelf of the study, within easy reach of my hand.
Now all I had to do was go back into Mom's arms and pretend to sleep, and the evidence would be perfectly erased.
Then I could claim a full alibi if I was questioned about what I was doing during that time. Fabricating an alibi is a basic technique, after all.
“Nihihi.”
✒️✒️✒️
‘What is Ayeon doing in the study?’
Lately, whenever she got the chance while we were napping together, Ayeon would sneak off and go into the study.
Then she'd come back and pretend to be sleeping again as if nothing had happened.
I figured Ayeon didn't want to get caught, so I deliberately pretended not to notice and let it slide, but now I was even more curious.
What exactly is she doing in the study?
There are only books there that would be hard for a child to read—specialized texts, general-interest books, classics, and the like.
Is she curious?
When I told that to my husband, he thought for a moment and answered.
“Honey. Our Ayeon has grown much faster than other babies. She memorized letters and words in no time.”
“Yeah, she did.”
“Honestly, isn't our Ayeon a real genius? Like a top 0.01%, Einstein-level genius. That's why she can understand hard books.”
“What? No, that's not it. Ayeon is fast, but still within a perfectly understandable range.”
“I have a hunch. I didn't mention it before, but when we named Ayeon, we got help from Ijun. We wanted to borrow some luck from a smart guy so our Ayeon could be born smart too. So maybe she's really incredibly smart?”
“R-really?”
I wasn't the sort to believe in superstitions like that, but when my husband said it with such a serious expression, something in me was stirred.
Oh no.
Moms on parenting forums get branded as obnoxious when they brag, ‘Isn't my kid a genius?’
It feels like I'm making that same obnoxious display right now.
In the end, I decided to put it to the test.
I grabbed a math book for early elementary students, far above Ayeon's age level.
“Ayeon, want Mom to teach you some math?”
“Sure!”
Ayeon came trotting over with a bright smile.
Come to think of it, I felt that Ayeon was like an angel.
Compared with the troublesome kids I heard about in parenting-forum stories, she didn't throw tantrums, didn't cry, and loved everything she did with Mom, so I was grateful that Ayeon had grown up so well.
“This is addition, this is subtraction, this is multiplication, this is division...”
“Mm-hmm! Mm-hmm!”
Ayeon listened attentively, nodding as I explained the four basic operations in the math book.
She had been the same when learning letters and words before.
She just nodded as if she wasn't thinking about it, but somehow Ayeon memorized everything after seeing it once.
After reading aloud the math concepts, I decided to ask the application problems one by one.
“What is 1 plus 2?”
“3!”
“Then what is 5 plus 4?”
“9!
“Want to try subtraction too? What is 7 minus 3?”
“4!”
“...What is 3 times 4?”
“12!”
“Division? What is 20 divided by 5?”
“4!”
My pen stopped.
After a moment of thought, I wrote an equation on the paper.
[x + 3 = 7]
No, that was going too far.
Let's not push it. We should start with the four basic operations properly...
Just as I was thinking that, Ayeon answered right away.
“x is 4!”
Just to be sure, I wrote another one.
[2x - 1 = 9]
“x is 5!”
“...”
My hand started trembling uncontrollably.
I wrote fractions. I wrote negatives. I wrote exponents. I wrote square roots. I even wrote differentiation and integration.
She got every single one right.
And answered instantly, too.
“...Ayeon.”
Before I knew it, my voice had cracked a little.
“Where did you learn this?”