would having a katana that uses finesse and has the two handed property be too powerful? Finesse two-handers don't make a whole lot of sense to me personally. Finesse says light, quick, flexible. Not something you need to manipulate with two hands for leverage and weight.
But by all means if it works for your tables, go for it!
— Dan Dillon (@Dan_Dillon_1) April 20, 2020
A katana wielded by an expert is capable of being used with finesse while parrying , and then powered in using strength through an engineered opening in the opponent’s defense. I would suggest allowing finesse in addition to two-handed only with the Blade Mastery feat from Unearthed Arcana: