Seiryu Rods are designed for catching smaller fish. They are very light and very, very sensitive. They are not intended for large fish, but if you fish for smaller fish in smaller streams they are just delightful. They take finesse to a whole new level.
Truth be told, they are not used for trout fishing in Japan. They are used for a number of smaller fish species that probably don't exceed about 8" when fully grown.The photo shows a fallfish, one of the larger "minnows" that inhabit the northeastern US and east central Canada (they get to about 20", although most are much smaller). If you fish for fallfish or creek chubs (perhaps the most underrated fish in the US - if caught on light tackle), or sunfish or little wild trout in little wild streams, you just can't have more fun than catching them with a seiryu rod.
They are like tenkara rods in that they are telescopic and the line is tied to the rod tip, but they are just so much lighter and so much more flexible. One of the most popular in the US is the Suntech Kurenai HM30R, which is 9'8" long and weighs less than an ounce. Fish it with 7X tippet. Fish it for wild brookies, or rainbows or greenbacks or redbands that live in the headwaters.
If the streams you fish are too small for a 9'8" rod, and some wonderful headwaters streams are, Nissin makes a 7'8" Air Stage Hakubai 240 that weighs 6/10 of an ounce. If you fish streams that are home to 5" and 6" trout, understand that with this rod they will put up quite a fight. Truly, it's not that small fish don't fight, it's that with heavier gear you can't feel it! With the the Nissin Air Stage Hakubai 240, you will definitely feel the fight. If you happen to hook the 10" king of the stream, your heart will be in your throat and you just might not win the fight.
Seiryu rods also come in longer lengths for wider streams. The Suntech Kurenai 33 and 39 are better suited for small (just not THAT small) and medium streams and also for ponds. For bluegills and modest crappies, and for trout of a foot long or a bit more, the longer Suntech Kurenai rods are just more fun than heavier rods.
A guy I fish with a lot uses the Suntech Kurenai HM39R. He uses it
for bluegills and small bass as well as for trout. He has caught
surprisingly large fish with it. I don't think I would use the Kurenai HM39R to target 14-16" trout, but if you are skilled at fighting larger fish with lighter tackle, you will win some (but not all) of the fights. The ones you lose will be some of the most memorable.
With the light tippet (no stronger than Japanese line size .5, which equates to 6.5X) and light line (either size 2.5 or 3) your presentations are more subtle and more delicate than you could achieve with any other type of rod. A seiryu rod is the only way you can out-finesse a tenkara rod. They are that much lighter and that much more sensitive.
The hooks are sharp.
The coffee's hot.
The fish are slippery when wet.