You can use a battery, a coil and a spark plug like device to ignite it, if nothing else. Don’t need a fuse.
The wire could also be wirewinding around critical components for additional strength. Blackpowder would have to be homemade as well as IIRC Japan won’t sell that at retail.
The thing is covered in duct tape. I wonder if he tested earlier versions to get it right. Probably did.
Wonder if the Japanese have access to Estes model rocket motors?
I fired a home made shotgun once out of a tube when I was a Yute, just to see if I could.
I used Sodium Chlorate saturated paper towels that I ran through a dehydrator rather than black powder wanting to go 100% non-conventional. (mom’s oven, long story there, the second time didn’t end well) and let me tell you it could have easily killed a man, I used a rocket igniter to set it off remotely.