This is a 20 meter spool of high-quality level line for your tenkara fishing. Cut your own lines to any length you desire. Multiple sections of line can also be connected when a longer line is called for. Chris Stewart has a useful page on level lines that shows the simple but unique rigging method.
You'll also need a spool to store your lines. These ultra-minimal, simple and inexpensive line cards work great for level lines. You can also use the Meiho spools or foam spools - either will slide onto your collapsed rod for easy carrying between fishing locations. The clip-on line winders we sell are great for furled lines but will kink your level line, so best to stick with the spools or cards.