Requested by @bismuthwisdom.
I'm going to start by saying that I do not think this is a good relationship for Gakushuu to start with. On top of that, like with Maehara, Ren needs time to settle down. And then, unlike Maehara, I think Ren is mostly straight instead of bisexual and much more prone to open relationships.
As a sidenote, I wanted to explain "mostly straight" because I feel it tends to be more overlooked than bisexuality in ways. An issue most bisexuals face is the assumption that when they start exclusively dating someone, they become completely gay or completely heteronormative, when in reality, they're still bisexual. It doesn't change just because they settled with someone. Then being mostly straight means that in certain circumstances, the person may occasionally be with someone of the same sex, but then people say "you're just straight". 🙄 No, we're straight with one or two exceptions for various reasons. For reasons I won't disclose, I align myself as mostly straight. I wouldn't want to date a woman, but I can appreciate their beauty. And mostly straight is where I think Ren is.
Ren is the kind of person that actively seeks out the beauty in life. The elegant curves and emotional depth of a person. I think this draws him more towards women overall, but of course these aren't exclusively women's traits, which is where the mostly comes into play for him.
I suspect that one of the reasons Gakushuu respects Ren as a person is because what's difficult for Shuu comes easily to Ren. The humanities, art, poetry. This subject has eluded Shuu up to at least the end of middle school and that is basically everything that Ren is. So, if GakuRen were to happen, I actually think Shuu would be the first to fall in love.
I see him keeping a close eye on Ren and making sure he doesn't get himself into too much trouble and sort of taking him under his wing to protect him. However, Shuu would need to go through a lot of changes. Before he can stop and smell the roses, he needs to slow down his race for number one first.
Ren on the other hand is very whimsical. He goes with the flow, follows the beauty. He likes to get lost and forget where he is, wandering from dream to dream, which is how he constantly finds himself with a whole other person at any given time. And Shuu is just what he needs to wake up.
I think this ship would take a long time to sail properly because it requires that Shuu grow as a person and then for Ren to grow as a person and then Ren needs to be ready to settle down and they finally confess their feelings to each other. It's also tricky because I feel Shuu would be the first to catch feelings, but Ren would have to make the first move. Meaning Ren would have to find out about Shuu's feelings without Shuu ever confessing them.
Anyway, so they'd be much older, which is fine because they'd easily remain friends throughout their entire lives, and here's a story for how it might go.
After Ren straightens up his act, he slows down enough to stop dancing around from woman to woman and actually start taking relationships seriously. He often writes love letters and songs and runs them by Shuu who then judges them and interrogates Ren about the person in question. This is Ren's trick to slowing down. If Shuu doesn't approve, he waits. And Shuu is honest about it despite his feelings for Ren because we all know how he internalizes shit because Shuu. I don't think that'll ever change. 😅
After years of this, Ren gets the whimsical idea to try and win over Shuu. Maybe as a joke, maybe as a challenge, but the letters end up being for him. And Shuu judges them without knowing this. Turns out, it's more than just a challenge. 😏
But Ren persists. He probably knows Shuu is gay and he's determined to make him fall in love with him, and then one day he realizes it's because he loves him back.
I imagine he fusses with this for a while because Shuu isn't the epitome of beauty, but the example of strength and control. Shuu's the complete opposite of who he usually goes after. But, you know, one day… he just decides to go for it.
Shuu attempts to keep his composure but he never expected in a million years to have earned Ren's affections, so the second Ren asks him out, Shuu lays out all the rules.
You're mine now and I'm not letting you go.
Perhaps it's more than Ren bargained for, but there's something alluring about the entire thing.
After all, there's nothing more beautiful than seeing a strong, immovable force going weak in the knees for love. 💙
And there you go! That's how I think it'd happen. I know it's a little different than how it's portrayed in other fics, but besides the fact that I only see Ren as mostly straight, I find it very difficult to see him actually wanting to settle down. He just strikes me as a wanderer. A gypsy. Sure, Shuu can inspire the best in him, but I honestly think Ren's best is a wandering spirit. Ren is forever chasing the beauty in life, hungry for more every second of every day. He's a free spirit.
I hope this interpretation is to your liking. Thank you for the ask!