"You wanted this necklace, am I correct?" Byakuya asks, holding a velvet box with a ruby necklace inside. "Don't answer that. Frankly, I know I'm right." He presses the jewelry box into your hands.

"Don't bother thanking me, I bought it so you'd stop annoying me." It's a lie to preserve his pride. He pays for everything, you don't even have to ask. He heard you wanted this necklace in passing, so clearly he listens to you.

Byakuya has the money anyways, and spending cash is his love language.