I'm curious, is this about Meiling having boobs & Remi doesn't or something like that?

It's just playing up on the gag of Sakuya being jealous of Meiling's breasts again. That's all.

(on that note, I guess it would be appropriate to tag this with breast_envy)

I am going the bet the tradition of knife throwing will be passed on

Sakuya calling Remilia "mother"... *faints with a happy smile*