I have noticed the Bond of Life stays for a long time (though it doesn't survive fast travel, sadly), which is definitely cool. I don't actually have a synergy team built around her yet, I'm just using her in one of my two daily commission teams to get her friendship score up, but I guess at some point I'll need to figure out some good units to pair her with.
Pyro has been my weakest element pretty consistently since launch, with Diluc being the only unit in that element that I've powered up, and that means that my pyro team comp has been less about elemental synergy and more about panicked berserk swinging of the sword from behind a shield.