Since this wasn't a problem that could be easily solved, nothing changed as we entered the summer vacation. I quickly finished all my summer homework, which now felt oddly nostalgic, so I spent my days either talking with my sister or playing the piano. I also read cookbooks daily to add new recipes to my repertoire and improve my household skills. Aside from grocery shopping, I barely left the house, and in this heat, even that drained a lot of my energy.
"It's really hot today, isn't it? The house is cool, but outside, it feels like a different world."
"Yeah, we need to be careful about our health."
"Definitely. Oh, how about we go to a pool or the beach? I've only ever swum during school classes, so what do you think?"
I thought it would be a nice way to cool off, and it's something I wanted to try, so I suggested it. But my sister made a slightly troubled face.
"Do you not want to? If not, that's okay."
"No, I want to fulfill your wishes as much as possible. Let's go together. Do you have a preference between the two?"
"Thank you. Hmm, I guess I'd prefer the beach. I've never seen one up close before."
"Alright, got it. Now, where should we go? I'll have to look up a good spot. Do you have any specific preferences?"
With that, my sister booted up the computer nearby and started searching for something.
"Specific preferences? Isn't the nearest beach good enough? Although, the less crowded, the better."
"Let's see… Hmm, unfortunately, it seems like the beaches around here aren't for sale. There might be some available on southern islands, though. Would that be okay?"
"Huh? Wait, what do you mean? We're just going to the beach, right?"
Why did this suddenly turn into a discussion about southern islands?
"Yes, that's right. So, we need to buy a property with a private beach. I checked, and it seems there are also houses with pools, so if you find a place you like, just let me know. I'll buy it."
She said this as if it were the most natural thing in the world, showing me the screen.
"W-Wait, why? I've never been to the beach before, but surely there are places where we can go without buying anything, right?"
"I can't allow anyone else to see you in a swimsuit. Look, how about this house? It has a pool in the garden, and while the beach is a bit narrow, it's private, so no one else will come."
"Oh, that seems… wait, no… Where are you getting all this money? I've never asked, but how do you even make money? You're not doing anything illegal, right?"
I couldn't believe she had that kind of money, and she's still a minor, so she shouldn't be able to work. She once told me not to worry about money, but even if she was getting some living expenses from our parents, they shouldn't have that much to spare. I started to worry that she might be involved in something illegal. To calm me down, she placed her hand on my head and gently patted me.
"I'm not doing anything like that. Really, Kaya, what do you think I am? I'm not that irrational. I just know what's going to happen in the future."
"And what does that mean?"
I knew things too, but I didn't see how that explained anything. Sensing my confusion, she explained further.
"I remember the winning lottery numbers for the next ten years, for prizes over 10 million yen. I also remember the stock prices and currency trends of major companies and emerging ventures for the next week. So, just by investing the money I win from the lottery into stocks and foreign exchange, I can secure enough money for us to live comfortably for the rest of our lives. So, Kaya, don't hesitate to ask for anything you want. I'll make sure it's all yours."
Even though she said that, I couldn't understand it. Knowing the winning lottery numbers for the next ten years? And remembering everything in weekly increments? That's an overwhelming amount of information. Well, she's my sister, so I guess she could do it. But if I relied on her for everything, I'd become useless, so I tried to find a flaw in her plan.
"But doesn't that kind of thing change if you do something? You know, like the butterfly effect?"
"The butterfly effect? You don't need to worry about that."
"Why are you so sure?"
"This is something I heard from Shinobu. Apparently, our ability has limits."
"Limits?"
"Yes. We returned to the past by dying. But this ability isn't a complete time-reversal power. It's more like rewinding time rather than resetting it."
According to Shinobu-san, the uncertain future exists as a multitude of possible paths. When the present catches up to that future, one of those paths is chosen, becomes certain, and links together to form the past.
Our ability, even if we go back to the past, can't change the paths that have already been chosen. Normally, even a slight change in our actions would cause the future to shift infinitely, but due to the limits of our ability, no significant changes occur up to the point we've already lived through. The actions of people not directly involved with us remain unaffected.
"Do you understand? Of course, if we act too conspicuously, there's a possibility things might change, but I'm managing that well. It worked perfectly fine in my second-to-last life. Though, since I'm not 18 yet, I can't open a stock or foreign exchange account, so I'm borrowing Shinobu's account."
"R-Really…"
I figured my sister had thought it through, but it was even more airtight than I imagined.
"So, don't let something trivial like money stop you from doing what you want. Understand?"
"Y-Yeah."
"Then let's pick a place together? Maybe we should choose somewhere far away and make it our vacation home."
"Yeah."
I just wanted to go swimming at the beach, so how did it turn into this? As I wondered about that, I pushed the thought aside and simply enjoyed picking out a place with my sister.