I've noticed that this fandom has a tendency to only focus on Akechi's side of the ShuAke dynamic. Even when it is focused on Ren, I only see people talk about the tragedy of their relationship or how it ends in the 3rd semester. That stuff's great, don't get me wrong, but I wish people talked more about their rivalry. It's one of my favorite aspects of ShuAke as a ship, and it reveals so much about Ren and Akechi as characters, especially when you focus on the jealousy between them.
Everyone knows that Akechi is jealous of Ren for a plethora of reasons (he admits as much in rank 8 of his social link), but I don't see anyone talk about Ren's side of it. It's like...people forget that it's mutual.
After Akechi's confession, Ren just...admits he feels the same way. His two responses to it are "Same here" and "Really hate losing, don't you?". The first response is Ren blatantly admitting that he can't stand to lose to Akechi either, and the second is Ren insulting Akechi and reminding him of his loss. The fact that Ren feels the need to insult him at all implies the same thing. But there's way more throughout the SL!
Ren refers to Akechi as his rival several times (which usually gives Akechi the most affection points, meaning he wants to be referred to this way), but it's also implied through his dialogue options. We can't hear his voice when he says them, but they still feel very...charged? Tense, might be a better word? They make it sound like Ren is invested in their competition, almost to the point of animosity. There's a genuine bitterness to his dialogue when Akechi underestimates him ("I see a lot of things" and "No holding back next time" are his responses to Akechi using his non-dominant hand in rank 2), and a genuine pride when Ren is able to get the upperhand in a competition ("You were getting cocky" and "You've still got a long way to go" are his responses to Akechi saying he wished he played better in rank 5). There's too much emotion behind them for Ren to NOT care, you know? He's not just going along with this rivalry because Akechi wants to, he's invested. He's not trying to match Akechi's freak, Ren's just normally a freak. This rivalry between them is mutual and Ren can't stand to lose to Akechi, and I can't think of why that would be unless there were a mutual jealousy between them. Why would Ren be so invested in beating Akechi, so determined to one up him, if he didn't feel that Akechi had something that Ren doesn't? He has to be jealous, at least a little.
But that brings us to the question of WHAT Ren is jealous of Akechi for. In my opinion, Ren's jealousy comes from 2 different places:
Firstly, Ren is jealous of Akechi's public reputation. Despite all the work he and the Phantom Thieves do, Ren and his friends will never be properly thanked for it, while Akechi is seen as a hero. Hell, depending on where they are in the story, Akechi opposing the Phantom Thieves makes him more of a hero in the eyes of the public. Ren's a showboaty theater kid who likes attention, so it makes sense that he'd be jealous of the positive attention, but that's not all. I really think he's more jealous of Akechi's LACK of a villainous reputation. Because of his record, Ren's seen as a dangerous, violent criminal by nearly all of his peers and teachers (except for, like, 5 people), and that reputation never goes away. No matter what Ren does, no matter how high his test scores are or how charming he is, kids always see him as dangerous and are too scared to talk to him. Judging by the face on his model in the real world, this frustrates Ren a lot, but he just kinda has to deal with it because of his record. Akechi would never have to deal with something like that. People admire him, respect him, LIKE him. No one's scared of him. All he has to deal with is getting spotted by fans who want an autograph ("Your life must be so hard" is one of Ren's responses to Akechi's annoyance at being recognized in rank 3. It's hard not to see the sarcasm behind it).
But that's not the biggest reason why Ren's jealous, to me.
The biggest reason is because Akechi has a future.
From the outside looking in, it seems like Akechi not only has a future, but a BRIGHT future ahead of him. Just look at him! At the age of 17, he's graduating highschool with perfect grades, early experience working as a detective alongside cops and prosecutors, and a celebrity status that has earned him a loyal fandom. At the age of 17! He has so many opportunities now, so many things he could do once he's done with highschool and his current work. He could focus on academics and get into a prestigious university, he could continue his detective work using his early experience and his connections to the police, he could just stay in the limelight as a local celebrity and make money off that alone for a few years. He can do whatever he wants! It looks like Akechi's future is nothing but bright!
...What will Ren do after highschool?
If he fucks up at any point, he'll go to prison. If he breaks his parole, if he gets expelled, if he gets sued, and so on, he'll be arrested. Obviously, if he's caught as the Leader of the Phantom Thieves, he'll go to prison for life, and that only becomes more likely as the game goes on. Ren knows full well that, if he messes up in even the smallest way, he'll spend the rest of his youth behind bars. He won't have a future.
Hell, even if he doesn't get caught, he still won't have a future. His initial arrest and parole are on his permanent record. His future employers will see it, his future landlords will see it, and how much do you wanna bet that they'll be willing to hire a criminal? Even if it's a false conviction, do you think they'd care? How hard do you think it'll be for Ren to get a real job in the future, a full-time one that will actually let him pay the bills and live in society? How hard do you think it will be for him to find an apartment, one outside of a dangerous neighborhood? Even if he does find a job and an apartment, that record will still follow his reputation, and anyone who finds out about it will see him as a dangerous, violent criminal. He'll still be alone. Ren doesn't have a future, and he knows that, all he has is the Thieves in the present.
But Akechi has a future; a bright future.
And don't you think that'd make Ren a little jealous? Akechi has so much going for him, so much to look forward to, and Ren will never have that no matter what. Ren doesn't hate him for it, he's not that kinda person, but he's still BITTER, and that's why he can't lose to him! If he loses to him, then Akechi just has another thing over him, and Ren can't fucking stand that! Ren doesn't hate him, he'd never trade places with him, he'd never give up his justice or the Thieves...but God damn it, he's jealous! He's just a little jealous, okay?
Now imagine how Ren feels when he learns that the jealousy is mutual!
Akechi doesn't really have a future to look forward to, he's probably just gonna kill himself once Shido's dead (since his entire life has centered around his revenge, I doubt he would keep going after it's finished). Akechi wishes he could've changed like Ren did, wishes he could've done something better with his life, and wishes he could've made friends. In his eyes, Ren has everything he doesn't, but Ren felt the same way, so imagine how he feels when he learns that! Imagine how he feels the more Akechi opens up in his SL, and Ren slowly realizes that they're not so different. Imagine how he feels once Akechi actually admits, with his own mouth, that he's jealous of Ren, too.
Can you imagine how Ren feels?
I bet it's the same way Akechi feels, when Ren says he'll hold onto his glove
