I know the scene after Ratio's "betrayal" can be read a lot of ways but I am shocked I haven't seen more people interpret it as Ratio being so worried about Aventurine that he couldn't stay away even though he was supposed to.
1) Ratio absolutely knew Aventurine's plan from start to finish, both his gamble to create "death" in the dream and with the three cornerstones. (Wish people would stop underselling Ratio in their analyses; "Three chips are enough" is a direct enough clue that, genius as he is, Ratio would never miss.)
2) In his own words, Ratio was acting according to Aventurine's instructions while in Dewlight Pavilion and with Sunday and felt that he did a good job not giving them away.
I think most people are on the same page up to there, but then I've seen a lot of people interpreting this scene after Aventurine leaves Sunday's mansion as Aventurine being genuinely angry at Ratio (possibly after having gaslit himself into thinking Ratio was actually betraying him).
But this doesn't make much sense to me because:
1) Ratio actually has nothing to gain by selling Aventurine out to Sunday. They're on the same side in this mission. Information about a Stelleron on Penacony wouldn't be news anyone with a brain like Ratio's and why would he need someone else's research on Stellerons when he already has ties to the Genius Society through Screwllum and Herta, as well as the Astral Express where the Trailblazer is actively housing a Stelleron?
2) One of Aventurine's most notable lines of dialogue is how it's perfectly fine and expected for "friends" to use each other and backstab. This is his default understanding of partners--why would he suddenly be mad about something he expected from the start?
3) If the betrayal wasn't already planned and was just a possibility based on Aventurine's understanding of Ratio, why would he ever have revealed there were "three chips" (aka three cornerstones) in play? If even the betrayal over Topaz's stone wasn't planned, just assumed, why would Aventurine reveal the existence of the third stone? He would gain nothing from doing so.
Instead, I think it makes a lot more sense to interpret Aventurine's frustration with Ratio in this later scene as annoyance over Ratio taking an "unnecessary" risk:
1) As far as Sunday knows, Ratio had just very seriously betrayed Aventurine, completely selling him out and essentially sending him to his execution.
2) In the scene afterward, Aventurine is out in public in the middle of Penacony where The Family's eyes are always watching, yet Ratio walks right up to him to check on him. Why would someone who just sold you out come up to you immediately afterward to check on your health?!
3) It's only natural that Aventurine would pump the brakes and go "Wow, didn't think you'd show yourself after you just betrayed me, remember?" Because that's the act they are supposed to be keeping up! They're still being monitored; it's not safe to break character!
But Ratio is a genius, right, so why would he break character here? From the standpoint of the ploy itself, revealing to the Family that he and Aventurine were still on the same side would only jeopardize the plan, not help it.
The logical explanation, then, is that Ratio went to Aventurine here because he felt like he had to.
He had to check in and make sure the situation was still under Aventurine's control.
(In fact, the entire exchange through the middle of this scene is Aventurine and Ratio confirming the rest of their plot in a veiled manner: Ratio brings up the plan and mentions what's concealed in the gift money bag, Aventurine confirms the cornerstone is good to go; Ratio asks what his next step will be; Aventurine says he's going to do the insane thing of handing out cash while looking pathetic [aka fishing for Sparkle]. Ratio essentially asks if he's crazy enough to take the final gamble with his own life, which Aventurine confirms, and then Ratio sets them up for the finale by gifting him the doctor's note.)
Ratio was willing to risk ruining their entire plan--something Aventurine does seem to be frustrated about at first--just to ensure Aventurine still felt all right about the situation.
He needed to deliver his note demanding Aventurine stay alive.
He needed to tell Aventurine to come to him if the situation got too painful to bear.
In short, Ratio was worried enough that he could not stay away even though, for the sake of their plot, it would have made significantly more sense for him not to appear. The gain of breaking character was worth more to him than the risk of being caught.
You honestly don't even have to take this in a shipping context. The real point here is that Ratio is an incredibly good person who wasn't okay with Aventurine's self-sacrificial plan and who felt morally compelled to check on a person in pain. He's a healer through and through, and ignoring Aventurine in this condition--ignoring someone who was taking so much risk on themselves--simply wasn't possible for him, no matter the danger it posed to the plan.
But for those who do ship Ratio and Aventurine... I hope more people will come to see this scene as another example of Ratio's genuine concern for his mission partner! He did not have to appear here at all; it would have made much more sense for him to leave Aventurine to his own devices to uphold the illusion of their "betrayal." He showed up in this scene--very likely against Aventurine's expectations--because he was concerned for Aventurine's situation and wanted to ensure Aventurine knew he could fall back on Ratio's support at any time if the plan went awry.
tl;dr: I wish people would stop interpreting this scene as the aftermath of a betrayal. Aventurine wasn't ticked off with Ratio in this scene because he felt like he'd genuinely been backstabbed; he was ticked off because Ratio was literally breaking their pre-established "betrayer" character just to be fussy over Aventurine's safety and well-being. (Okay, and to double check on the plan, but let's be real, the first part was definitely more important. 👌)
