The Tenkara Level Line has a small diameter so you want to use a light tippet. You want your tippet to be lighter that the line. When you fish with a Tenkara level Line you are fishing a “tight” setup. Meaning all the line is kept off the surface of the water by holding your rod tip up and keeping the line tight. Only your tippet and fly should be touching the water. At least this is the case with dry fly or traditional kebari flies. Since Tenkara Level Line is 100% fluorocarbon, it will sink if laid on the surface of the water and will drag your dry fly down. If you are using nymphs that you want to sink below the surface, it’s not an issue. I would suggest using 7x, 6x or 5x tippet. 4x will be big for the Tenkara Level Line….you might be able to get away with it.
Depending on where you are fishing, if the trout are small, 5x or 6x should be fine. &x if the fish are really spooky or get pressured a lot. The bigger the number, the finer and smaller the tippet.