I had no idea Rui was actually going to get at the end and thus retrain... well all the memories, and though I'm totally glad about it because he had a hell of a development (I'm not sure if it was noticed from the outside, but on the inside, he was forced to change a lot), for a large part, this means his personality is going to change massively. This is a general thing to point out Rui's impressions on the plot, what changed him, and how he's going to deal with things from now on.
Note it's 10 A.M. and I still haven't slept so if it's make no sense and there's Deliese DEAL WITH IT
Now first of all, rereading my Rui app, it sucks ball. I left a lot of stuff I had in mind since... forever ago, because it was stuff so obvious to me that it didn't even occur to me to mention. Well, it's mentioned, but very vaguely, so. To make things short, Rui is very much two faced. He can be a jerk, he's mischievous, he likes to have people do things for him and you know what, he likes to be the one manipulating things and make them go however he wants. In a way he's worse than Delaine, because he's subtle. Honestly speaking, though? Rui isn't even really that bad. he isn't as defensive and it's actually easy to get to befriend him, if you click, he'll stop being a bitch (assuming he's not acting like a cute boy), or at least be a bitch only occasionally. He talks a lot, says a lot of mean things occasionally, but doesn't really have any real ill intent behind it. Everything else should have been mentioned in the app, but if you spot something he does often that is not, please let me know and I'll add a clarification.
Now, onto how the plot affected him. Like everyone else who got involved, Rui was forced to deal with a ton of bad situations. Negative emotions, positive emotions, despair, fear, hope, and so on, he went through a lot. Now other than the MUST SURVIVE setting itself, what has shaped him the most here was Isao, which is kind of lulzy because he hated his guts at first. Now, let's point out that Rui doesn't like people who look like TOUGH GUY and so on, which his why he immediately had a fight with him. There's also a mix of envy, because unlike him? People like Isao are strong. Rui sees them as people who can have everything without having to fake being someone they're not. This is one of the things he kept shouting when he was fighting with the group in demon harem-- he was emotionally unstable and Isao's speech just made him think that he was not like him and could not be that strong.
At the same time..? Isao protected him and his group. When Rui actually got his balls out and distracted Matador, trying to prevent him from killing Isao, he got complimented. Isao told him he did a good job, and also that he's brave..! In the end? If Isao hadn't complimented him and confronted him in a manly way the second time, Rui would have given up. He didn't because his words affected him greatly. Naoki's last moments also had a huge impact over him.
So, what is he going to do from now on? Rui is going to try to be more true to himself. He will try to be able to bear not being... you know, loved by everyone. Because he wants to endure it, and because he wants to be loved for who he really is. He's tired of faking, and he realized he was because of the plot. Does it mean he'll stop being cute and adorable with people? No, not completely. Obviously it'll probably be a very gradual thing, and not something easy for him, because it's something he's used to, but he wants to try even if the results end up being horrible.
Furthermore? He wants to be more brave. He wants to believe in himself a bit more and maybe, one day actually have a talk with his parents, telling them how he feels. That part is not likely to happen anytime soon, though, as he is terrified of the idea of hearing them laughing at him for that or, well, just ignoring him.
In short, Rui is definitely going to change.
As far as trauma goes, he's going to try to look at the whole experience in a positive light. He will feel like a terrible dick for leaving people behind and such, but he's happy everything got resetted, and knows that maybe? If both him and Ageha didn't make it, it wouldn't have been enough.