[Akame]

It's a great katana but its not the absolute choice, there are katanas that amount to the same amount of power in terms of swords. Hisen, Hakouhen, Raijin, etc... I wouldn't put it above any of those. So I don't think the scaling or the weapons stats are a problem. Vydel procs too frequently and easily. And it's not affected by silence. By changing it to a charge effect like Slydria stated it would take some time to achieve the effect.

Pretty much this.
I do agree though that the base power and accuracy of the weapon should be toned down a bit, but the scaling is fine as-is. Things like the Spine Leash exist still with a high 120% scaling, so the Tarnada's scaling isn't too out of hand. I think a slight tone down on the base power and accuracy, combo'd with Sly's idea should do the trick for the Tarnada to keep it in check.