A lot is the usual problems of derivative fan fiction in getting author permission and trying to portray a 'canon' character accurately knowing for certain that their creator will look. And then reading, in-depth, the relevant stories to learn everything there is to know about the battling style of a character.
More that they occupy a tier between the HOLY S*** OP BADASSES (Keith/Criss, Gideon to an extent, Jane) and the rather weak (Eve, Andrea, Alaska, Sai). There just aren't a lot of mid-journey characters right now, which is about the power level yours fall into. Maybe Reggie v. Gela from my own work could work, although I have no idea how much experience Reggie has with dealing with OHKO moves. If it's fairly little... well, she's getting at least one instakill in that match. Probably more. On the other hand, Gela would have zero idea how to deal with Chigon and outside of her Gyarados and OHKO moves she has no real power to work with. So it's stuff like that the series would have to consider.
More that they occupy a tier between the HOLY S*** OP BADASSES (Keith/Criss, Gideon to an extent, Jane) and the rather weak (Eve, Andrea, Alaska, Sai). There just aren't a lot of mid-journey characters right now, which is about the power level yours fall into. Maybe Reggie v. Gela from my own work could work, although I have no idea how much experience Reggie has with dealing with OHKO moves. If it's fairly little... well, she's getting at least one instakill in that match. Probably more. On the other hand, Gela would have zero idea how to deal with Chigon and outside of her Gyarados and OHKO moves she has no real power to work with. So it's stuff like that the series would have to consider.