Mavuika has never had to think about her own safety as Archon because there’s not a lot of people who could come close to her power. I mean yeah there’s the rest of the Seven but they’re all in dire straits at the moment too.
The closest to her strength is probably Ei but that is a long way from home and there was never any reason to fear her because they’re in similar situations;
The heroes of Natlan would never do that to her, and her people are loyal because she treats them well, there wouldn’t be anyone who would start a coup, and all of them are united against a common enemy even with their differences: The Abyss
The only party that has ever been a threat was the Abyss because Natlan was closed off from the rest of the world
There was never really a pillar she could lean on, even as a kid (her character stories are actually kind of sad, she was the one Parenting her Parents even when she was like 5, and then she had to Parent her Sister on top of all that)
No one was her equal, and no one treated her as an equal--not her friends, not her family. She was put onto this pedestal, and she had to carry all of it alone, and she thought that was normal and completely reasonable to expect of somebody at her level (which, if we're talking about Mavuika level, is probably the highest and only level there is)
So when Capitano comes knocking she doesn't think much of it... Until their Stadium fight. She then realizes. Oh Wait. An Equal? A Threat Aside From The Abyss? What The Hell?
So now she has to think about her own security because this beast of a man is after Her and the Gnosis She Is Keeping. Now people around her are talking about security details and guards around the Speaker's Chamber when she's never had to before and Mavuika is in a full-blown existential crisis. Just a lot of:
I’ve never had to think about this for myself, surely this is not needed?
…Why haven’t I been thinking about this for myself?
Should I be thinking about this for myself?
Capitano's entrance is the first time she had to consider her own safety and well-being aside from winning. Like yeah if she dies fighting against the Abyss that's fine as long as she made sure that her people won, she can just revive anyway! Broken bones are nothing with her healing factor, it might hurt like a bitch but she'll be back on her feet again next time, ready to die again for winning!
But with Capitano it's a rude awakening of: Oh fuck I might Actually die in Real Life fighting against This Person? And Actually I'm Needed by My People beyond just fighting the Abyss? Oh I have a Purpose outside of Fighting and Being A Warrior? I have to be a diplomat, a representative, dealing with tribal disputes outside of Abyssal related incidents? Strength and power aren't the only things that define me? Oh Shit! I have to stay Alive and protect Myself From This Threat!
TL;DR: Capitano is the perfect foil for Mavuika because he's her Equal and her Enemy. So Now she has to think about Herself for once