Depending on the story, the Kaibas' ages are malleable. In one of my stories, Noa is the eldest brother. In this one, however, Seto is still on top of the pyramid, and that makes him the patriarch of the family.

What this means in the context of there being three Kaiba brothers is simple.

Noa and Mokuba are his children.


.


Noa's idea of a day in the city was a whole different beast compared to Ryo's. Noa liked to spend his time watching people, and that was the entire crux of it. That was all he did, all he wanted to do, and he would often forget to do anything else; even the errands which brought him out into the city in the first place. So it was that, after such a day trip, Noa often found himself famished, and dehydrated, by the time he walked back through the front door of Kaiba Manor; every time this happened, Seto would give him a disapproving look and Noa would promise to do better next time, all the while knowing that he wouldn't.

It wasn't that Ryo disliked any of Noa's favored hobbies. It was just that, for Ryo, the day wasn't complete unless he found something nice to eat and somewhere nice to eat it. He didn't always buy a little something for himself—like a new book, or a tabletop miniature, or a comic, or a movie, or a videogame—but he usually did. This became especially true by the time he and Noa started going on dates in the city, since Noa's wallet was a much more powerful artifact than Ryo's would ever be.

Noa wasn't sure about this, but he guessed that that was one reason Seto was so pleased about Noa's relationship. He didn't think his elder would have been nearly as interested in the whole affair if not for the fact that Ryo was so hell-bent on making sure that Noa made healthy decisions when they were together.

It wasn't that Seto was uninterested in Noa's life as a matter of course; it was simply that, much like Mokuba, Seto only had a passing interest in, and knowledge of, Noa's various hobbies. He knew enough to understand either of his brothers when they talked about them, and he knew enough to ask the right sorts of questions to keep the conversation going. That was usually the end of it, however; Seto viewed this as part of his job as their guardian, and he was dedicated to it, but Noa and Mokuba were both too sharp, and too familiar with Seto's mannerisms, to not notice a hard limit to his interest.

On the subject of Ryo, though, it was different.

Seto was keenly interested in any development in Noa's bond with Ryo, to the point where—even if Noa passingly mentioned his name—he would put down whatever he was holding in his hands and turn his entire attention on his brother. Given that Seto was the poster child for ADHD's maladaptive habit of never stopping his activities no matter what was happening, this wasn't just noteworthy.

It was a miracle.

Noa wondered what to make of this fact; he knew well enough that Seto and Ryo didn't really talk much. They never had. They would cross paths every once in a while, and that was all. They'd been classmates; they took AP History together in their third year of high school, and AP English in their fourth. They both liked collecting various things.

But Seto's interest in Ryo now was almost entirely to do with Noa.

He asked Mokuba about it once.

"What?" Mokuba asked, looking dumbstruck with disbelief. "One of his kids has a boyfriend and Niisama isn't supposed to pay attention? Come on now."