Thats funny. I think we aren't so familiar with these characters and their still-establishing canon to make calls like "OOC"-- we are still in the process of learning how any of them respond to situations.

They are equivalent to someone you've only known for a few days, in a small set of circumstances, through a tiny window-- with the only additional perspective added being what we know of UNDERTALE (which will be discarded by people who do not feel Ralsei is Asriel, thus he's as unknown as Susie).

In most of the circumstances we've seen, Ralsei has had a lot of control and oversight. We haven't truly seen him agitated or provoked ... he's mostly been ignored, or only briefly regarded by King, Queen, and Tenna. Nobody has ever antagonized him meaningfully, beyond the childish and uninformed ways Susie and Lancer might... nothing that gets under his skin. Nonsense, shenanigans, only.

For whatever reason, Flowery is the first character to be VERY familiar with Ralsei, and not at all shy to flaunt that intimate knowledge. Ralsei's facade is laid bare by Flowery, who knows him to be a liar. Flowery challenges Ralsei's control over how others perceive him, and how he presents his narrative to others, and even the control over explaining mechanics and lore. For whatever reason, this control is incredibly important to Ralsei. But then, isn't it to most liars? That is why they lie.

This is kind of embarrassing maybe to say, but my favorite quote is from the webcomic 10%+, "you never truly know someone until you've seen them angry." I think about it often, in both real-life conflicts and fictional ones. I've known a lot of people who were one way typically, and completely shockingly different once they were truly angry at someone or something. It can be a jarring experience. You can know someone for years and years in an amicable light, maybe see them a bit annoyed ... and be completely blindsided by their anger when it finally shows. This kind of insight can destroy trust or friendships quickly. It can completely change your opinion on someone! Whether it is pointed at you, or someone else.

I think there were hints all along that Ralsei has a guarded edge, and a judgemental, snippy side! He's BEEN exhausted, bored, annoyed by interactions before! I think people see him as completely submissive and gracious, because that is how he acts towards Kris, and Susie's (childish, insecure) disrespect means so little to him. His regular "okay." when something happens has always been catty to me......! Very, "whatever". To name just one thing, the Spamton situation is a clear one where he is rather detached and judgemental of the darkner at hand (I recall a lot of people at the time feeling suddenly mistrustful of him after this scene). He's not always charitable, compassionate, or empathetic ... which I would say is rather on blast when you do things like Attack Everyone NOW as Kris. He values Kris above the comfort or safety of any 'darkner'. He will try to correct Susie from being harmful, but of course Kris can make of these worlds what they will. These darkners are not nearly as much 'people' to Ralsei as they are to Susie.

These worlds aren't important or valuable to him. The people inside of them are an experience to share, not individuals.

I'm me so I'll also have to talk about the Asriel contingency, as nobody else on the planet will: of COURSE Asriel fucking hates Flowery! Chara's favorite flower was the golden flowers! They drew a picture of them, which Asriel hung near the bed. In DELTARUNE, the same image of a golden flower is above Asriel's bed... this fondness for the flowers must be both cute and maddening!

I think if Kris has a favorite ANYTHING, Asriel/Ralsei will be jealous and feel insecure, LOL. Kris loved to 'talk to' the flowers... I wonder if Asriel was jealous of the words granted in secret to the flowers, what they knew of Kris that he didn't! Of course the flowers are more annoying and threatening to him than some stupid dice and playing cards! One must be gentle, delicate with flowers, care for them. Imagine how helpless an obsessive person could feel! The pretty, nice-smelling flowers...!!! It's so simple to be a pretty flower and have Kris find you beautiful!!! You don't have to constantly try!!!! MARIGOLD THE GIANT RAT!!!

Even people into UNDERTALE alone struggle to accept Flowey as insight into Asriel's heart. That Asriel has this jealousy, insecurity, desperation, cruelty, inside of him... of course, I see it as an essential aspect of the incredible love Asriel had for Chara. "to confine desire to what holds sweetness; how small desire would be". (:

As for Susie, she's had such a linear and visible journey of being domesticated, I've no idea what would seem 'OOC' about any of her actions... she's had so many of these misadventures now, she knows to not demonize or react impulsively to any darkners, after so many have become her friends, and share an innocent goal of wishing to exist in this dream. If she stayed helplessly 'consistent' she'd be like.... a character in a cartoon that isn't allowed to emotionally evolve due to the non-continuity of the given canon, like a Squidward or a Land Before Time child. Squidward will always be sour, Petrie will always be fearful. Susie is meant to progress through a narrative that is actively changing her. She will come out the other end different.

Besides, we see her defensive side rear back up when something triggers her. Noelle & Kris riding the ferris wheel in Weird Route (and Noelle closing in on Kris) causes her to launch a dirt clod at their cart.

While Ralsei has shown us peeks into a distant, unempathetic side lying beneath his sickeningly sweet facade, I feel Susie has always done the complete opposite. She externally expressed a cruel, judgemental side as a defense mechanism around her much softer, lonely interior.

I believe all characters in DELTARUNE express this duality in one way or another, as a core tenet that will serve the theme of the story overall. You don't know who Ralsei, Susie, Noelle, or Kris, and likely Dess, are at a glance (in a way, wasn't that also half of the point of UNDERTALE?). Their responses to situations may surprise you. What they are capable of remains to be seen!