Diana suddenly went from the person closest to a breakdown to the most stable one of the three. It makes sense, she's a knight at heart, I'm just surprised. It also seemed like she felt she can't win as long as Lapis is playing but she can't give up on either her friend or her crush. Typical hero.
Is Natori even aware the two younger girls are talking about romancing her? It's not like the situations recently allow much alternative readings, and the words are loaded. It matters a great deal to the themes whether Natori is carrying the idiotball or if she completely recognizes the horror and self-denial Lapis is facing.
I keep going back and forth on whether Natori knows that Lapis has actual feelings for her (of the kind that go beyond "close confidant/servant"). I'd have to go back and re-read everything, but I feel like I remember it being made somewhat clear that Lapis actually Liked her when they were at the mining town/facility.
My problem (and it's not necessarily her fault, especially if she's actually unaware of Lapis' feelings), is that Natori seems oblivious to what Diana feels for her. And the fact that she's so effortlessly close and touchy with Diana is clearly eating away at Lapis, to the point that this failed bet was made on the match without Natori's knowledge.
I'd like to think that, if Natori
did know that Lapis had actual feelings for her, she'd not be a moron who still got all touchy-feely with Diana right in front of her. Hence my suspicion that she's in the dark about it. (Which, would suit Lapis fine, since she's resigned to her death upon completing her goals concerning the Noble/Commoner rift, and she'd not want to get close to Natori only to lose her, or however she herself phrased it a couple chapters ago.)
But I guess I'm operating under the assumption that Natori is "carrying the idiotball" as you stated, because her behavior around them both would make ZERO sense otherwise, unless she's secretly a conniving heartless bitch (all evidence being to the contrary).
I'm pretty sure she's aware of what lays in Lapis' future though, since she played the game and thus should know the ending for her employer. The fact that she doesn't seem to be making moves at present to push back against that is strange to me, unless she's just trying to be nice and change Lapis' mindset toward commoners bit by bit without outright thwarting her.
Which, seems like a bad idea, but....maybe we need more plot/events to take place.
The prince's right hand person remains a problem in general, though, since I feel like his goals run counter even to Lapis', even if he's ostensibly aiding her on some things. He's a shifty motherfucker, so I hope whatever's going on with him gets revealed and addressed before too long.