Sashiko needles are extra hard and sharp. They come in several different lengths (e.g., the shorter ones from Clover which you can buy here) for different types of sashiko stitching. The longest needles can take a bit of getting used to, but they are practical for long straight stitches because it's faster when you can load many running stitches onto the needle before pulling the thread through. Sashiko stitching can also be curved and have many different patterns; in that case, shorter needles are advisable.
You use a special thimble, which you can buy from the brand Olympus here, or handmade by the family business @llittlelemonloom here.
The needle has a relatively large eye to accommodate sashiko thread, which is quite thick.
As far as I can tell, two of the needles in this pack are the same as the two in the 2-pack, but here you also get a medium size and a needle that is somewhat shorter.
Sashiko thread can be purchased here.
Instructions for sashiko will eventually be available on this website, but it will take some time. Many have wanted sashiko equipment for a long time, so I choose to sell before I can provide instructions in Norwegian for those who want them.
Search for sashiko on YouTube, and you will find some good help! There are also dedicated sashiko groups on Facebook, for example, and several handicraft associations offer sashiko courses, so check a handicraft association near you if that's of interest!
The book Mending Matters also covers some stitching inspired by Japanese handicraft techniques.