The Tenjo Line is the uppermost section of a keiryu or ayu fishing line. It can serve several purposes, but I generally use a Tenjo for visibility and to reduce tangles. Thus, I choose a hi-vis line that is a bit thicker than the rest of the keiryu line.
The main benefit of the hi-vis is that it is easy to see and it effectively points to your markers, making them easier to spot at the very beginning of your drift. The main benefit of having a slightly thicker line is that it reduces the chances of tangles at the rod tip.size 1.25, 30m spool