After getting confirmation that the weapon I asked about in this thread I made , I'm wondering what the stats of a nagamaki would look like, since they're not in the Corebook and don't appear to be in other supplimentary materials. Should I just reflavor a no-dachi or naginata? Or should I attempt to homebrew it, and if so, how would I best balance it?

The style is similar to the nodachi, it has reach but the blade isn't much greater than the katana. For the weight and additional leverage, you might give it +1 Damage but Cumbersome, so the profile is a bit more like the Naginata, but it is still a sword-type weapon.

In another thread its suggested to make it the Zambato. I think this makes a lot of sense as the weapons blade is straight but curved at the striking edge like the Nagamaki and with similar grip, reach, just a different blade geometry. The actual Zambato is nearly the same weapon as a Nodachi and should use the same stats. Nodachi blade is curved all through its edge like a Katana.

The Nagamaki's biggest advantage is its long shaft that offers better leverage when wielded two-handed but also allows the weapon to be wielded one-handed. Since its blade is - AFAIK - a normal sword blade, it does not really compare with the larger weapons like the Nodachi or the Zambato. It would be more like a Katana that gives +2 Damage when wielded two-handed instead of +2 Deadliness, and has Wargear instead of Ceremonial.

Note that, in these rules "Damage" translates to 'how much effort it takes to avoid this' and "Deadliness" is more like the actual damage done to something after you connect.

Yeah, I reckon by wielding the Nagamaki with both hands you would attack harder and not kill harder.