So it is a katana with yellow and green sheath.
But you will find another katana also share the same sheath that called "Wasabi".
Wasabi is with a round hand guard.
Matsukaze is with a square one.
Check first if you want to draw your weapon.

The maximum value you can get is :

Attack 5
Defense 25
Weight 0
Quality 8

If value close enough, I suggest you keep it first.
Then if you are looking for the perfection, just start another round.

1. open a new round with instant kill mode

2. go to Posting Station and save your game there just in case if you get killed

3. keep switching map until you see a guy named Ikema who lay on ground in the middle of street

4. Ikema got high chance carry Matsukaze. If he's not carry it, just switch map and return. He will change his weapon randomly.

5. Once he carry Matsukaze, kill him and loot your Matsukaze. See if the quality good enough to keep. If yes end this round, and maybe next round for best quality depend on you. If not just load your save and go back to step 3.