A detail that's important to me is that Susan is on a blanket. She would not be comfortable just sitting on the floor. She much prefers there be something between her and where people have walked around with their feets

And no, "feets" is not a typo. YOU say "feet". I say "feets".

Catalina, meanwhile, has become one with the floor, and has unknowingly reduced her chances of getting Susan hugs even further than normal.

Speaking of where everyone is sitting, my in-story excuse for them all sitting around the board like that is Hanma being present and observing their game. I would absolutely have them doing that even if she wasn't there for panel staging purposes, but HUZZAH! I actually have an excuse for them doing so!

Hanma's age (and immortal ages in general)

Immortals default to an adult form when resetting, both mentally and physically. By human standards, it would sort of be like a ninety-year-old person suddenly being around twenty again in every conceivable way (including memories), but with a sort of notebook filled with key details of the past seventy years added to those memories.

To the point, if immortals ever were babies who needed to grow up, they got that done with millennia ago at a minimum. That said, they're still potentially losing out on a LOT of maturity and character building by resetting. Seriously, just imagine meeting the you of several years ago, and think of everything you know now that you didn't know then.

It can be safely assumed that Hanma wound up adopting her preferred younger form and sense of identity from, and I know this is shocking, spending a LOT of time at anime conventions.

Trope?

I don't actually know if that's actually considered a trope. I just know it seems to be a thing? Maybe it's not? Whatever. It's a trope in anime within the EGS universe.