I couldn't find great pictures of the swords but that gave me some freedom to play around with some of the details.
Since I am a lot shorter than Natsu, I scaled the swords down so I could translate the cosplay to my body type.
I knew I needed something relatively light and easy to work with so I used MDF for the scabbards. The handle of the swords are also MDF. The blade is actually made of poplar because poplar is much easier to sand than oak or plywood; at the same time, it is rigid, I don't want a floppy blade haha. I drew the swords on Illustrator first, just to get my ideas finalized. I decided that I wanted the scabbards to have beveled edges, and the handle to be an elliptical shape. I guess if you look at the in-game screenshots the scabbards have beveled edges? There was a lot of math involved while creating the scabbards and the blades in order to have the blades fit snugly.
After the bases were created, I began painting the scabbards and the swords. I used Montana Gold for the red--I actually used up half a can!! Fumes everywhere...
For the handle, I wanted to do something a little different and give it a stone-textured finish. I bought a stone-textured finish spray from Home Depot and applied that over the primer. It takes 24 hours to fully dry, but the effect looks really cool! I sprayed the red paint over this to finalize the look.
I had already decided ahead of time that I would be sculpting the details on the scabbard with clay, and creating the details on the handle with Wonderflex. I didn't feel it was important for the details to look perfect on both swords; I wanted these swords to differ slightly in the details. I used lightweight stone clay--dries faster and easy to sand. I kept the sanding to a minimum because I knew I wanted to apply a brushed gold finish afterwards. The best way to create this brushed gold look is probably to apply black paint to the surface you're working on, then use a dry brush to apply the gold paint on top of the black base. If you have too much gold paint on an area you can quickly wipe it off with a damp towel or brush. I used acrylic jewels for the accents. For the less "organic shapes" on the scabbard I used Wonderflex for structure and stability. Then came more clay for the twisty-vine details. For the twisty-vine details on the scabbards, I used black puffy fabric paint. All of these were given the "brushed gold" treatment as well.
For the sword handles, I used Wonderflex for all the details since it would be easier than sculpting, and especially since these pieces were very thin to begin with it would be easier to add layers of Wonderflex rather than to roll out a ridiculously thin piece of clay, only to have it break later.
I used more black puffy fabric paint for the raised details on the swords. Then gave them the "gold treatment".
These probably don't look like they took FOREVER, but the fabric paint took at least 20 hours to fully dry, and I had to lay the scabbards completely flat while I applied the paint otherwise it would drip. So I could only paint one surface at a time! Stone clay also dries fairly quickly but I still had to wait at least 4-5 hours in order to start applying paint. Lots of time spent waiting for things to dry!!
4/1 edit --I mentioned on Twitter that I was going to break down the cost of this cosplay, and I realized I didn't write that here. I am only including things I had to buy specifically for this cosplay, not leftover materials:
2 strips of poplar = $2/ea, $4 total
2 3/8" pieces of MDF = $2/ea, $4 total
1 can of stone finish spray = $9
1 bottle of puffy fabric paint = $4
1 sheet of 21" x 27" Wonderflex = $33 (after shipping)
1 can of red paint (leftover)
1 can of metallic silver paint = $6
1 lb of lightweight stone clay (leftover)
2 bags of acrylic jewels = $3/ea, $6 total
1 tube of gold acrylic paint (leftover)
1 tube of black acrylic paint (leftover)
TOTAL = $62