Kotoko is the stupidest girl he's ever met. She proves to grow stupider each and every single day. Yuuki feels bad for Uncle Shigeo; having such a stupid daughter must be insulting.
Especially when Uncle Shigeo is a great man. He always makes good food, always smiles, and he is a really good driver. He even drives Yuuki to school sometimes, tells him he's got employees that work real early and employees that work real late.
He likes Uncle Shigeo.
Yuuki cannot (and will never) say the same for Kotoko. She is insufferable. She forces him to call her Sister Kotoko, forces him to listen to her 'jokes', and even keeps him up at night with her crying. His bed is adjacent to her room — his old room! — and she sniffles constantly.
At first, Yuuki had thought she had a very bad cold. His mother had always told him that girls are weaker, more fragile than men — and although Naoki, exasperated, had sat him down, pointed to his biology textbook, showed him the identical skeletons — Yuuki still thought that was the case.
Mama's influence is staggering.
But no. That was not the case. Kotoko is weak, yes, but it is not because she is a girl.
No. Kotoko is weak because she is stupid. But even the stupidest person in the world would not cry because they are stupid, right?
Hm. Perhaps she's crying because she is stupid.
That would make sense.
Even so, Yuuki does not feel bad for her in the slightest. Not in the slightest way ever. It is good that she is self aware. Perhaps than she will take her studies more seriously. She should be like him.
Yuuki is always studying with Naoki.
In the same room.
Not actually studying with Naoki.
Naoki never teaches him anything, really. Not in a serious way, really.
Naoki only corrects Yuuki, only corrects his homework, and even then there's rarely any mistakes, so Naoki just leaves him alone for the most part. That is always saddening, because there is so much to learn, there is so much Naoki knows and Yuuki would really like to be a part of that.
It is okay, though, because Naoki will always be with him. Naoki will always be around, even if he doesn't teach Yuuki directly.
There's other ways to learn, right?
That is what Yuuki always tells himself when he studies by himself, without Naoki's help.
So it is a shock when Naoki is studying with Kotoko. Yuuki is even more shocked when Naoki shuts the door to his old room, and when Yuuki listens in, lays his ear against the door, it is confirmed.
Naoki is actually teaching Kotoko!
He snickers when he hears Naoki yelling at Kotoko. Soon, Naoki will realize that it's pointless, and then he will return to their room and forget about ever teaching Kotoko. Maybe he will be thankful that Yuuki is so smart and he will apologize for always ignoring Yuuki.
He sleeps alone the next night, waiting for Naoki to return.
Apparently, Yuuki is not the only one who is shocked. Everyone else — Mama, Papa, Uncle Shigeo even — are shocked to see the two studying. The house has grown topsy-turvy once again, just because of that stupid girl causing a fuss.
The next night, and the next night, and the next night, Naoki does nothing but help Kotoko study. Yuuki still feels lonely in his room, but it has been going on for long enough that Yuuki has grown used to it. The alarm goes flickers in the dark room, and it's just bright enough that he can see Naoki's bed, empty.
He misses Naoki, hates Kotoko for stealing him away.