Which line?

Your loving spouse just gave you a nice, brand new tenkara rod for the holidays.  The first question you are probably asking yourself – What kind of main line do I need to start fishing?

The good news/bad news is tenkara rods tend to be pretty versatile in being able to cast and fish a wide variety of line types and sizes. Ask 25 anglers what their favorite line is, and you'll end up with 30 different options.  It’s not surprising when you think about it; you are using a relatively long rod to cast a relatively short line. 

First fork in the road - furled or single strand line (there are also some hybrids).  From a simplistic perspective; if you tend to mostly fish dead drift, single strand is probably the way to go. If provides a much smaller cross section, hence less drag. Less drag, better dead drift.  The converse, if you prefer a more active presentation (skate, swing, skitter, twitch, etc) a furled line is probably a better option.  With a larger cross section, it is easier to use things like the current and the wind to manipulate your fly.

If you decide to go single strand, you are much better off fishing fluorocarbon, rather than monofilament. Fluoro tends to be both denser and stiffer for a given diameter, so it tends to cast better than mono.

I will say a good furled line pretty much casts itself; they are very pleasant to fish.

When it comes to talking about the string stuff, a key point is to make sure you consciously make the tippet the weakest link in the chain. It's a must when fishing a fixed length line set up in order to prevent damage to the rod.  Fishing a light tippet may cost you a big fish or two, unfortunately that’s one of the few downsides to fishing a fixed length line set up.

The best advice I can give you, pick an option and fish it for a bit.   You'll soon find out what you like (or don't like) and you'll be able to zero in on the right solution for the way you like to fish.