Sashiko needles are long, rigid, and very sharp. They are designed to let you "load" multiple stitches on the needle before pulling it through the fabric.
They come in various lengths. Shorter needles are easier to handle, so they are a good choice for beginners or for when you are stitching curved lines. Longer needles let you load more stitches, so they are good for straight lines. They take a little getting used to, but once you get the hang of it, longer needles can make your stitching go faster.