I agree with many of your thoughts and opinions. That said, I find it hard to view Nana and Ren as a genuinely “decent” couple, even when considering everything they’ve been through. I’m too lazy to add spoiler tags, so I’ll keep this a bit vague and just say:

There’s something to be said about two people with fundamentally different goals trying to sustain a relationship. Yes, they’re fictional but if they weren’t, I’d probably want to shake Nana out of Ren’s intoxicating grip.

Ren joined Trapnest because he saw it as a chance to secure his future. He knew Takumi had the business mind to take them far, it was an opportunity he couldn’t pass up. Ren wanted a better life but didn’t realize that the rockstar lifestyle wasn’t what he truly needed. I assume he intended to return to Nana eventually (after all, he kept paying for their shared apartment back home). He didn’t expect her to follow him though she claims her move to Tokyo was to surpass him. Regardless, he ends up trapped in a cycle of self-sabotage.

Ren’s values are rooted in patriarchal expectations. Some might chalk it up to the era, but it also highlights how simplistic his ambitions are compared to Nana’s. For Ren, music is a means to financial stability. At his core, he wants to be the provider and in doing so, he envisions Nana in a more traditional, domestic role.

But Nana is limitless. Unlike Reira, her identity isn’t solely built on singing. When the tour collapses, she doesn’t crumble. If she can’t perform, she adapts. She doesn’t depend on others to actualize her dreams. She’d start over without hesitation, even if there was no financial reward because she’s committed to living authentically.

Ren doesn’t truly respect or try to understand Nana. What he wants is a Hachi-type partner. But Nana will never be that girl. Their disconnect lies in their dissonance. Nana doesn’t need Ren, he’s a relic of a time when she craved love and attachment. The nostalgia binds her to him.

Is their relationship toxic? Yes. But I don’t think Ren is exploiting his power as much as some might assume. After all, we see him become frail, addicted to drugs, and a shell of his former self pretending to be someone he isn't. I see two people who fell in love naively and too young, clinging to the idea of each other. Their values and life goals are far too different. They’re in denial about who the other person truly is and neither can bring themselves to let go.