These girls are going to reclaim that "focus" of his, and his sister is being absolutely no help back there. If anything her face is screaming "be sure to give me lots of nieces and nephews now, dear brother" I wouldn't be surprised if she instigated it.
It's hilarious how Ayaka and Keqing are getting ready to dish out some punishment while Eula and Shenha are like "you could have just said you wanted to see tits"