Collapse the rod and wind the line around a spool that slips over the rod. It's actually much easier to carry a tenkara rod along mountain streams and in thick brush then it is to is a rod with a reel and guides. Another advantage.
I will add that 10 foot (non-tenkara) rods are fairly common, and 11 footers are available. They're popular with Euro-nymphers, and I like them for upstream wet fly fishing. I seldom fish tenkara, but I can see the advantages for some streams.