I've started filling up the panel lines of my RG redframe's katana sheath, and above is my progress on it. At time of posting I've actually finished the whole thing but don't have a photo for it yet.

I used a Sakura Pigma Micron 0.003mm pen for the black panel lines.

Here's part of what it looks like now:

The original katana sheath looks like this:

It's just white and red with some sticker decals along with a 'golden' tip. I saw the next photo somewhere in the web searches. It's a good take on customizing the sheath but I wanted mine to be a bit rugged and dark. Also, I don't have a gold spray paint. I only got a silver and red metallic one. And a flat clear.