I'm having a hard time identifying the type and era of this sword. Family-lore says that it came from Japan prior to WW2. Any advice or suggestions would be appreciated.

Steel blade: 29 ½ - inches long from guard to point; 0.21-inch thick blade at root, tapering to 0.12-inch at mid-point before coming to a sharp point. Back-curving blade is 1-inch wide at hilt, then swells to 1 ¾ inch wide before coming to a sharp point. Blade is sharpened starting 6-inches from the hilt. Two pairs of blood-grooves on each side, with brass inlaid circle between each of the four segments. No visible grain or temper line. No visible signature or symbols stamped on the tapered tang. Dragon is stamped on both sides of blade, approximately 5-inches long; open mouth.

The oval-shaped guard is steel and appears to have once contained an insert, opposite the sheath. Wooden split-grip covers the tang; wrapped with natural-color braided rope. Brass-colored band at the guard end of handle. Steel pommel has small hole aligned to the tang.

The scabbard is wooden with ornate black lacquer-and-wire finish. The scabbard’s bands, harness attach bracket, and end-cap are steel.

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sword and scabbard, right side

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sword and scabbard, left side

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hilt

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dragon, right

It's a Chinese single handed dao and definitely not from Japan, since it's illegal to own one there.

Like Lancelot says, it's a Chinese dao.

Specifically, it's a niuweidao AKA oxtail dao. It's a civilian sword rather than military. The niuweidao becomes common in the 19th century, so it's a recent type of sword.

These can be hard to date, since they were still made well into the 20th century in this style as martial arts swords. Niuweidao are still made today as martial arts swords, though the usual modern ones are somewhat different in style. Yours looks very late 19th century or 1st half of 20th century. The spiral-wrapped scabbard is old-style (even the modern fake antiques that are supposed to be late Qing in style don't usually have scabbards like this).

Some examples:
http://www.swordsantiqueweapons.com/s1822_full.html
http://oriental-arms.com/item.php?id=2516
http://mandarinmansion.com/niuweidao-oxtail-saber
http://mandarinmansion.com/quality-niuweidao
http://www.antiquechinesesword.com/saber-dao
http://www.mandarinmansion.com/chinese-oxtail...reign-mark