The Sakasa Kebari, or reverse hackle fly is probably the iconic "tenkara fly." Dr. Ishigaki's fly is a variant, using rooster hackle rather than the more traditional hen pheasant soft hackle feather. I tie the sakasa kebari with partridge. The partridge feathers wrap well, they are the right size, and on one skin you get both brown and grey feathers.
I am struck by the similarity of the Japanese fly and the Italian pesca alla Valsesiana flies. Both have reverse hackles, and both flies are "worked" or "manipulated" when they are fished. The reverse soft hackle pulses as the Japanese use their "invitation" technique and as the Italians "dibble the top dropper." In both cases, the slight motion of the hackles gives the impression of life, which can be much more effective than a plain "dead drift" presentation.
The pesca alla Valsesiana flies are also somewhat similar to the North Country style of soft hackle flies, although they are more heavily hackled, tied on curved rather than straight shank hooks, and often use silk floss rather than silk thread for their bodies.
Like the Valsesian flies, Sakasa Kebari are hackled much more heavily than the North Country flies. I think that is a key design element. The sparse hackles of North County flies will fold back along the hook shank when the fly is worked. The hackles of the Sakasa Kebari open up rather than fold down when the line is pulsed. The hackle shape, and the heavy hackle, act like a sea anchor or drogue chute (an underwater parachute), resisting the pull of the line. That helps minimize line sag and allows a tenkara angler to keep his line tighter and off the water's surface.
The Italian Valsesiana and the Japanese tenkara both utilize long rods with light lines tied to the rod tip. I do not believe that it is coincidence that anglers in both counties developed reverse hackle flies by coincidence. I think the rod, the line and the fly act together as a system, with the reverse hackle shape being an integral part of that system. Not all traditional tenkara flies were reverse hackled, but many were and are to this day.
The step-by-step sequence here shows such a fly, tied with a partridge feather for the hackle and Pearsall's Hot Orange Gossamer silk thread. I'll often use a brown feather for both the Partridge and Orange and the Partridge and Green, and a grey feather for the Partridge and Yellow and the Partridge and Red (which is not a standard pattern, but is and adaptation of Michael Hackney's favorite brookie fly, which uses a red thread body and grizzly hackle).
1. Start the thread at the eye and wrap back about 1/4 of the way to the bend. For a size 12 or 14 hook and Pearsall's Gossamer silk thread, I use 11 wraps.
2. Strip the fuzz off a partridge feather and tie it in on the top of the shank with the concave side up and the stem extending out over the hook bend. Do four or five wraps toward the hook eye, snip off the tip, and wrap to the hook eye. Then wrap back to the feather, lift the feather, and do about three wraps behind the feather.
3. Wrap the feather with each wrap just behind the previous wrap, being very careful to not trap any barbs with your wraps. After each wrap gently stroke the feather barbs forward. Unlike the North Country one to one and a half wraps, make three wraps for a partridge feather, three or four with a hen pheasant feather. Tie off with three or four thread wraps. If you have wrapped the hackle properly, it should already have sufficient forward slant. Tying it off often traps barbs on the wrong side of the thread (toward the bend). Clip these off.
4. I now tie in a collar of peacock herl, Takayama style. Take one herl (preferable from a Peacock Eyed Stick rather than strung herl) and holding it with both hands, catch the tying thread.
5. Lift the herl behind the hook and gradually place it on the top of the hook shank, with the tying thread just behind the hackle.
6. Make about four touching wraps with the thread to secure the herl. Wrap the herl about three times, then tie it down and clip off the herl on the bend side of the thread.
7. Wrap back to just before where you want the body to finish, and then back to the herl. Finally, wrap back to just beyond where you finished the body (by about three wraps), then do a four wrap whip finish with each wrap in front of the previous one. That should complete the smooth body. Trim your thread at the very end of the body
Photo shows fly tied on a Daiichi 1250 barbless hook.
In addition to orange, which is perhaps the most popular "Partridge and ..." color, tie them also in yellow (which is an excellent imitation for sulfers), green (for any of the caddis species in which the pupae have green bodies), red (to see if Michael Hackney's favorite brookie fly becomes your favorite as well), and both peacock herl and pheasant tail because flies with those materials just seem to catch a lot of fish.
Don't think they're just for trout.
Bluegills can't get enough of 'em.