I wouldn't say that as harshly as Rain is, but I'm honestly not finding good information to make an accurate length and weight in reference to Tanya's strength. The blade is long and heavy and sharp, enough to make Tanya have difficulties wielding it properly without the enchantments. I'll confess the picture isn't accurate to its length because I botched my attempt at foreshortening, it's almost as long as Tanya is tall.
I feel like anything I try and guess at would probably not be very logical in respect to Tanya's physical strength and the blade's size itself, mostly because I'm really not that knowledgeable about medieval weapons. I mean, my best knowledge comes from occasionally seeing them in a museum and Dark Souls, which isn't exactly in-depth.
Most swords of Repharion's approximate length rarely exceeded three and a half to four pounds, and that's on the larger side. It's harder to guess without knowing an exact blade shape. Most swords aren't as heavy as you'd expect.
The real problem comes from the enchantment to make it more lightweight; "most of its weight being negated" implies it weighs as much as a switch. The lighter a blade is, the less impact it carries when it strikes, meaning that Repharion wouldn't be able to batter armored enemies- a vital tactic in armored combat. Without weight, it's also impossible to knock a blade aside or parry, meaning your defense is diminished greatly.
Slicing would also be a trickier matter without some weight to the swing. A Japanese sword, for example, is designed to be great for slicing, but they're actually thicker and therefore heavier than a European sword of the same length.
Moreover, a nearly weightless sword has no sort of feedback, which means you risk overextending and hurting yourself when you swing it. Jedi also have weightless swords, but this problem is countered by them being psychic.
