These early chapters don't correspond to anything specific when it comes to canon. They're mostly meant to introduce the stakes and set things in motion. As this story unfolds, we will be seeing various canon events and how they change based on what's changed.
But mostly, "At Sixes and Sevens" is a glimpse into the lives of a couple kids trying to make it in a magic-saturated sitcom.
It's much more "Paved with Good Intentions" than "Kick a Hole in the Sky," if you take my meaning.
.
"So then . . . okay, remember I told you about the chef's complete obsession with that potato salad, right? Acted like it was the Holy Grail of side dishes and woe betide anyone who said otherwise. It wasn't even very good, to be honest. Too sweet. I mean, okay, Seto liked it, and that's basically a miracle, so I guess I should give credit where it's due. But anyway—"
Mokuba was cut off by a sudden, sharp ringing that felt like a blade slicing into the air. Ryou flinched, confused for a moment, until his companion flashed an apologetic look and reached into his jacket. Mokuba came out with a smartphone that probably cost more than Ryou spent in six months, put it to his ear, and his face assumed an expression that would have looked more at home on a king at war.
"Kaiba," Mokuba snapped; even his voice had taken on a royal identity.
Ryou tried to go back to studying, thinking that the day was probably shot as far as prepping for an exam went, but he couldn't manage to maintain any semblance of focus. He kept wondering, as he listened to his new acquaintance—friend?—talk, whether or not Domino City would be any different. Any better. Whether this school would stay standing after Ryou had attended for more than a month. Whether these teachers would do anything but shy away when Ryou entered the classroom. Whether this police force would—
"Stop with the jargon and tell me!" Mokuba almost shouted, and suddenly the tension in the room felt sentient. Ryou blinked several times, felt his breath grow heavy in him, and had to bend every faculty he possessed to maintaining a calm façade.
The shadows in the room, faded into nothing while Mokuba had been laughing and gesticulating randomly with his hands as he soliloquized, were moving. Ryou could see them, like insects; like tiny reminders that moving to a new city—no matter how big, how bustling, how densely populated, how bright—didn't banish the ghosts of old memories.
As Mokuba's face shifted again, into a look of crestfallen shock, Ryou Bakura thought he could hear a voice, a familiar voice, whisper into the back of his head that it was happening again.
Already.
It was happening again.
". . . Thank you," Mokuba murmured softly, lowering his gaze to the table, then staring into the patterns in the wood grain. "I'll be right there. No, that's . . . that's fine. I'll drive myself. You know what to do."
Mokuba slipped his phone back into his jacket, stood up, and drew in a deep, steadying breath. "I have to . . . cut this one short, Ryou. Sorry we didn't get to the actual studying part of the program. Gotta get home."
"What, um . . . what's happened?" Ryou dared to ask, licking at his lips as his insides shriveled up like a desert. "Something . . . serious, I take it." He berated himself for saying something so patently obvious and stupid, but he'd always had a habit of being unable to properly articulate himself when he was nervous.
Mokuba's eyebrows raised. "Yeah, I'd . . . say this is serious."
A pause.
"My father's dead."