"You don't have to whisper. Your voice is soft enough not to disrupt the audio," Kaiba responds plainly, but still with his tone kept quiet. The only reason he's doing it is because using his usual voice apparently made the audio crackle, and Mokuba had given him more than enough shit about it that now he moderated his tone!

He has no idea how it might be affecting his passenger, and it didn't matter, right?

"Secure yourself. I'll be takin' off in a few moments."

Yuugi should consider himself lucky that the cockpit dome is only now sliding shut with a pneumatic hiss, otherwise Kaiba might have looked at him in the reflection of the glass and seen him being highly affected by...Kaiba talking?!