RP is a Collaborative Hobby: A PSA
Most of us roleplay because we have characters we love and want to explore. It's entirely natural to want our muses to have exciting moments, important arcs, and meaningful character development.
However, roleplay is a collaborative hobby. It is not something you write alone.
It's okay for some threads to focus more heavily on one character. Sometimes you might want to have a thread where your muses solves the problem, where they're injured and taken care of, where they're worshiped by their love interest. There's nothing wrong with that.
The issue comes when that becomes the default dynamic, and one person's muse is always the center of every plot while their partner's character exists mainly to support their story.
Your partner's muse deserves to exist as a character and not just a supporting role. They should get to have their own goals, conflicts, relationships, and moments to shine. They should not just serve as an accessory to make your character's story more interesting.
This applies not just to letting them be the hero, but also letting them be vulnerable. Sometimes certain characters become known in a community for being protectors, leaders, or the person who always has things under control. While those traits can be a big part of a character, it can become exhausting for a writer if their muse is constantly expected to be the one who saves everyone, understands everyone, or takes care of everyone else.
Even characters who are strong, capable, or highly experienced can face major issues, and the people who write them would often like to explore those softer or more troubled sides too.
The same principle applies to AU and crossover verses.
They are both great ways to explore new possibilities and interact with new characters. However, they work best when everyone involved still has control over their own character's identity.
When making a verse, make sure you ask yourself if you are creating a shared story or simply asking someone else to play an NPC in a story that is centered around your muse.
It is not fair or appealing to your partners to do things like
Making your muse responsible for another character's major life events.
Rewriting another character's backstory so it revolves around your muse.
Making your muse the center of the verse and the only one who can solve things.
Those are the kind of things that need to be planned out ahead of time with your partner.
You also need to be careful when making a verse where your muse has pre existing connections with canon characters. There is nothing inherently wrong with this. In a lot of cases, it would be really hard to slot a character into a different fandom and have them never encounter any of the canon cast.
However, there is a massive difference between your characters having simply met before, or having a connection like being coworkers or something, and hard-coding a canon character into your muse's backstory as someone they have a deep, unshakeable connection with, like lovers or family, without your partners consent.
On a side note: There is absolutely nothing wrong with making an OC or an alternate version of a character and giving them a connection to a canon character, whether it be friends, siblings, lovers, or a child. But you should make it very clear on your blog so people who play those canon characters can look at your profile and decide if they wish to interact with that specific lore.
Before introducing a major AU concept, it may help to ask:"Does this give both writers something interesting to explore?" and not focus on just what you find cool for your muse.
Roleplay is not about one person getting to tell their story while everyone else plays NPCS. It is about building something together.