Like with any project, this starts with milling up some pieces flat and square. I'm going to use some lightly figured hard maple and Peruvian walnut 

Layout
The layout and sawing for this joint are pretty punishing. There is no room for error at all. I am using about an 8 degree angle for the dovetails. I mark both pieces at the same time. Here I measured where I want my pins and tails to be based on the width of the board and to make sure I can sneak my smallest chisel in to remove the waste. I make a knife nick on both boards with a square

From that knife nick, I use a bevel square to knife in my angles. The layout is fairly simple once you do it a few times. From the center of the two boards, lay out the pin/tail closest to the edge first. The angle goes out toward the edge of the board, from the top. After that the angle goes toward the center of the board. 

Now I mark the other board matching up the center lines 

Then I mark the waste on each piece. This is the first  nejire kumi tsugi I did in poplar, but it shows up better on camera as the walnut is a little dark

Once done with the top, Transfer the layout down the sides of the board. Again like with the top, start at the edges and go from the center to the edge using the same bevel square used before. Then the next set of pins/tails go in the opposite direction This layout is critical. Sawing has to be spot on 

Now I saw the joint to my lines staying barely inside the waste. This is difficult because of the compound angle. There are no straight cuts at all. Like mentioned above, sawing is critical. Paring the waste leaves a lot of opportunity for error because there are no 90 degree faces at all. You want this joint to fit right off the saw.  
Once done I remove as much of the waste as I can with a coping saw

On the pin board, the edges need to come off. I use a wide chisel to make a ledge for the saw to ride in and stay true

Then carefully saw the waste. Remember that the tail is at a compound angle so sawing straight down will cut into the tail. 

Once done I move on to sawing the pin board. Again it's critical to stay barely inside the marked waste when sawing.

Even removing the waste is done at an angle. I am using a 3mm chisel there. 

Once the waste is chopped out, I put the piece back in the vise to pare down the floors to get the waste hiding in the corners

Assembly is quite tricky. This is a video of my test joint going together. There's no persuading with a mallet possible here. If the angles are not exact and complimentary, the joint will not fully seat as it goes down and forward at the same time. 

Completed box in the background with the pins and tails flushed up. There are some gaps but not bad enough from preventing me from making a lid and slapping some finish on it. I'm looking forward to perfecting this joint, it's pretty fun