So I know there are people who hate it, but I am one of those people who indulges in "skinny little character has a massive sword because magic". Personally I'm of the opinion of "listen, if people are allowed to have dragons that have forelegs AND wings (how the hell do the bones and muscles work for that?), and if zombies can have eyes intact enough to see after more than like...two days (makes no sense, do zombies decompose slower than normal bodies?), and if people can grow spikes or claws and then have them go away (wait, where does the mass come from? Where does it go to!? Are they made from calcium, does the person need to eat a lot of cheese to maintain this power!? How does this even make sense!!?) and if people can conjure fireballs (a friend of mine calculated the energy involved in this. It is er.... enough to destroy the world. Even for a small firebolt) I'm allowed my silly big swords, okay!?"
So yes, Rekki is a 5'3"/160cm woman with noodle arms who probably weighs just under 50kg and she has a sword that quite possibly weighs more than she does. It's a ridiculous sword and she has a silly fighting style where she just kind of flings herself at things and uses the momentum to just cleave through. So you'll tend to see in terms of fighting pose, Rekki is all about big movements. Her punches are always hyper-extended in a really reckless way, her stances tend to be big lunge stances, and when she swings her sword, it tends to be a big arcing swing from the shoulder.
If you've done any martial arts, you'll probably realise, this is actually a fighting style that in real life wouldn't suit a 5'3" woman with noodle arms. Being myself a 5'1" woman with noodle arms, my own fighting style is nothing like Rekki's. I studied Wado-ryu karate, a form of karate with shorter stances than shotokan and and emphasis on being light and mobile rather than powerful. I specialise in feints and kicks, usually backstance because I have a low centre of gravity. My sensei was a big scottish guy who was always like, "Now listen, ye cannae punch them or ye'll just break yer wee chicken bone hands. Just stun 'em with a kick and run away."
If Rekki was sensible, since she has a similar build to me, she would fight this way too...
But Rekki Lune is a doofus who unfortunately has been gifted so much magical super-strength that she can use what is actually worst style of fighting for her and still keep winning.
It's part of Rekki's personality though, that she over-relies on magic and makes poor decisions. On the other hand, there's also an element of power fantasy here, because when you're a small woman, you can't just fight like that, just go wild and fling punches, so it can feel quite freeing and fun to have this character who is just cutting loose like BOOM! I think it's something the audience like about Rekki.
So yeah, sometimes for character reasons or fun spectacle, I have chosen to deliberately have my characters fight in ways that aren't strictly practical, and that includes fighting in a style that doesn't suit the person's build.