The Phantom Thief Boys and Emotional Intelligence
You can split the male members of the Phantom Thieves down the middle based on how they deal with their emotions. Morgana and Akechi bottle up their feelings, while Ryuji and Yusuke are very openly emotional no matter what they feel, and Ren is in the middle.
I'm starting with Ryuji, since I think this is an underappreciated aspect of his character. Throughout P5, Ryuji always say what's on his mind, even when it gets him in trouble. You see this the most with his anger (Kamoshida responds to this by breaking his leg) and frustration (complaining about Futaba's shadow in her palace, which comes across as a little insensitive), but Ryu's pretty open about everything else he feels, too, in a way that feels very mature for his age. During the 2nd rank of his social link, Ryu opens up to Ren about his physically abusive father, the way Kamoshida triggered that memory for him, and the way that he still haunts Ryu and his mom to this day. In RANK TWO. In any other social link, that would be rank 6 at least, maybe 8 or 7 even. And it clearly still HURTS Ryu talking about it, he's still furious about everything, but he still feels comfortable sharing that. A part of that comes from how close Ren and Ryuji are even at the start of the link (their awakenings happen just so they can save each other, platonic soulmates I tell ya), but that's still such an intimate detail, such a personal thing to share with a boy you've only known for a month. And Ryuji speaks too clearly for that to be a new subject for him; he's thought about it before, a lot. And even outside of this moment, Ryu is always open in his link about what he feels, especially about how happy his friendships with Ren and the rest of the Thieves make him. He says Ren makes him feel "free", and Ren makes fun of him for that every time because it's cheesy, but Ryu still says it. He always says what's on his mind and he's always open about what he feels.
Yusuke is a parallel to him in this way, because he's also very authentic about his passions and emotions. Neither Ryu or Yu ever pretend to be something they're not, even when it gets them in trouble or isn't seen as proper (Yu tells a Yakuza member that he has the spirit of a flailng pigeon, for example). Unlike Ryu though, Yusuke doesn't have as much understanding over his own emotions. His SL centers around his conflicting feelings over his artistic passion, his pride, and the love he still feels for Madarame as a father despite his abuse. It's all confusing to him and causes him a lot of grief. But despite that, Yusuke is STILL always open about his emotions. No matter how ugly he thinks the feeling is, he never tries to hide it from Ren, and instead seeks out his aid. He even seeks out help from Ann and Ryuji, and shares with them what he believes is a disgusting emotion. It's confusing, but he tries to actually work through it rather than hide it.
Ryuji isn't practically intelligent and Yusuke is very socially aloof, but despite that, they're both very comfortable with their emotions, no matter how "embarrassing" or "ugly" they are. They never try to pretend to be something they're not and never change themselves for other people. It gets in their way sometimes, but they're very emotionally mature and clearly happier for it.
Now contrast that with Akechi and Morgana, the "smart" ones. Chi Chi and Mona are both practically intelligent and much more socially conscious than Yusuke and Ryuji are, but in comparison, they're both TERRIBLE at dealing with their emotions. They're both insecure and bottle up their emotions until they literally explode out of them.
Straight up, the Okumura arc only happens because Mona doesn't tell anyone what he's feeling. There's at least 5 seperate scenes where Morgana gets close to asking Joker for help, both in his SL and the main story, but he backtracks and goes "nevermind, it's nothing" every damn time. Ryu only called Mona useless on accident, he would never do that on purpose, but Morgana chose to hide how much that actually affected him until he literally couldn't anymore, which led to his massive crash out. If he asked for help at any point, they would've supported him, but he didn't, he just hid it all. I think it goes without saying that the same thing applies to Akechi. The main difference between the two of them is that Chi Chi bottled it up for even longer, and it exploded out of him more violently as a result.
Another similarity they have is that, despite both going through major shit as a result of them bottling up their feelings, Akechi and Morgana STILL do it afterwards.
During the descent into Mementos, Mona's insecurity about his humanity starts to flare up and Haru can tell. But instead of opening up to her, he just keeps hiding it. This doesn't end badly like last time, but it's still sad that Mona hasn't changed.
In the 3rd semester, while Akechi knows the truth about Maruki's reality and knows what will happen to him when it's fully destroyed, he still keeps quiet about it. A few days before 2/2, there's a dialogue between him and Ren at the station where Ren asks what Akechi will do once Maruki's reality is destroyed and Akechi says "I don't have to tell you" with a smirk on his face. Then he forces the conversation to keep going so he won't have to tell him the truth. His relationship with Ren is the most intimate one Akechi's had in a decade, and he still hides it from him. He obviously has a reason for it, but it's still painful and dishonest (imagine if Maruki didn't tell Ren. Imagine if Ren destroyed that reality and only found out what happened to Akechi afterwards).
Akechi's also the only Thief whose 3rd awakening isn't in his room, and that doesn't feel like a coincidence. He's the only one who still can't share private stuff like that, even with the man who wished him back.
Ren fits into these parallels in an interesting way; he's a middle ground between the two. He's harder to read than the other boys because he doesn't have much dialogue, but I think there's enough for a solid analysis.
Unlike Ryuji and Yusuke, Ren is both practically and socially intelligent. We all know he's practically intelligent because he's the Leader, but you can also see his social intelligence in his dialogue options. Ren has A LOT of stupid dialogue options, but basically all of them read as Ren consciously making jokes rather than genuine misunderstandings. He knows how it sounds when he says Ann's codename should be "Sexy Cat", that's why he said it, he knows how it sounds when he says "Honey, I'm home" to Akechi when he found him at Leblanc, that's why he said it, etcetera. Ren isn't actually misunderstanding the situation, he's just making dumb jokes to be funny. Another point for Ren's social intelligence is that Akechi considers him smart. In his SL, Chi Chi compliments Ren on how observant he is and generally regards Ren as an intellectual equal. Considering how socially conscious Akechi is, I don't think he'd would regard someone socially aloof as intelligent (see the many times where Akechi calls Ryuji and Yusuke stupid to their faces in the Thieves Den). Ren can pick up on social cues, mood of the conversation, and people's real intentions pretty easily, unlike Ryu and Yusuke. However, unlike Akechi and Mona, I wouldn't say that Ren hides his emotions either. He's a quiet guy and keeps things close to his chest, but still, I don't think he's hiding.
Ren's arrest is something that canonically traumatized him. His hands shake when he signs the lease for the DVD shop, because it reminds him of signing his false confession, and he's clearly distraught when he gets dragged away to the police car in the flashback. Unless he has to, Ren doesn't tell people about his arrest, including most of his confidants. Almost everyone who knows, they know because they have to (Sojiro) or because someone else told them (Mishima). It's still a fresh wound for Ren and he doesn't like sharing it.
But Ren tells the Thieves.
He tells Ryuji about it in the Beef bowl place, when Ryu's confidant awakens, and he tells Yusuke at the hot pot they have after Madarame's palace. I don't remember when he tells Ann, but she knows, and he tells the rest of the Thieves near the end of the game when he finds out that Shido was the man behind his arrest. He even tells Akechi about it during his rank 4. Every time, the Thieves meet Ren's story with incredible compassion, but I think people overlook the fact that he TELLS them willingly in the first place. He doesn't...have to, you know? Especially not early on before they find out about Shido. When they ask, he could brush it off or say that he's not comfortable sharing, and they'd be fine with that, but Ren CHOOSES to tell his friends what he's dealing with. It's a traumatic story and he doesn't like telling it, but he has no problem sharing it with the people closest to him.
Ren does hide stuff, but not everything. I think looking at Ren's actions as a student vs. his actions as a Phantom Thief says about this balance.
Ren, as a student, is isolated from his peers, a constant subject of nasty rumors and seen as intimidating no matter what he does (kids call him a punk when he gets an answer right in class, no matter how high his social stats are or how long he's been there). Judging by the uncomfortable and angry expression resting on his model in the real world segments of P5 (look it up, he looks so pissed off all the time), Ren hates being judged like this. It sucks, generally, but it could also get him in trouble with the police, and if that happens, Ren goes to prison. So he tries to mitigate the damage in any way he can. Unlike his friends, Ren wears his Shujin uniform exactly to the dress code, so he doesn't stand out more. He wears fake glasses so he'll look less intimidating. He even slouches so he won't be so tall. Ren is clearly very concious of how he's viewed and hides a lot of himself when he's a student.
But when Ren's a Phantom Thief, he doesn't hide anymore.
He's cocky, brash, rebellious, goofy, and has a MASSIVE grin on his face the whole time. In the Metaverse, he uses his Persona, the manifestation of the rebellion that always sleeps within him. He's the FIRST person to awaken to his Persona, the first to embrace this dangerous side of himself for the greater good. It's a badge of honor. As soon as Ren is in a palace, as soon as he doesn't have to worry about being arrested anymore, Ren doesn't hide a single part of who he is. The greatest irony of Persona 5 is that Ren is most free when he dawns a mask.
The way Ren acts as a Phantom Thief makes it clear, to me, the difference in why he hides what he feels sometimes. Morgana and Akechi hide what they feel because they're insecure, but Ren hides what he feels in the real world so he won't get arrested again. The mask he wears as a quiet student isn't to cover up an insecurity, it's just so he can survive. If he could be as free as Yusuke and Ryuji, he would. And when Ren doesn't have that pressure, when he's running around as Joker and spending time with closest friends, he is free. He doesn't need the mask anymore. In those moments, Ren shows what he feels, no matter what he's feeling.