Much like we westerners like Japanese food, but alter it to suit our tastes, Japanese people like western food, but often with a Japanese twist. At the Uomo subway station in Tokyo, there's a little bakery full of western-style breads (OK, there are actually tons of such bakeries), where you take a tray and neatly fill it with pastries from the display (with tongs, of course). Here it is that we discovered green bread -- green tea flavored, to be precise, with ribbons of sweet azuki bean filling. And it was excellent.
In Japan, green tea and sweet beans are popular flavors for many things, but for some reason, it hasn't caught on anywhere else I've ever been. This means if you want these flavors, you'll have to make it yourself.
It so happened that I had a surplus of sweet azuki beans (well, I made mochi  and cooked way too much azuki filling), so I decided to try to recreate this bready Japanese wonder.
I started with a few different brioche recipes, and while I originally had been planning to go all out and pack in the butter, when push came to shove, I couldn't bring myself to use more than 3/4 cup.
The result was pleasantly sweet, silky soft, and while the green tea wasn't overly prominent, the beans went very well.
This quantity of dough works well when split into two 4-by-8 inch loaves (or several smaller buns) -- after the bread was done rising and baking, each pan was about 80% full.
For two smallish loaves:
3 cups flour
2 teaspoons yeast
1/2 cup milk
2 tablespoons sugar
2 tablespoons matcha green tea powder
150 grams butter
1 cup cooked azuki bean filling (1/2 cup azuki beans, soaked for 24 hours, then cooked until soft with 1/4 cup sugar and a pinch of salt, and lightly mashed)
First, mix together about half a cup of flour, the milk, the sugar and the yeast. Let sit to proof -- you want it to get all bubbly.
Then, work in the rest of the flour, the matcha powder and the eggs. Slowly incorporate the butter -- the batter will wind up being much wetter and stickier than your standard bread dough.
Leave the dough to rise, until it doubles in size.
Punch down the dough, and knead/mix it again. Now you'll want to shape the rolls, and add the azuki beans. It might be easier if the dough is cold.
Roll out the dough into a flat rectangle (or two), top with beans, and roll up. Give the roll a twist for added interest. Let the loaves rise until they're a good size (for an hour or so, but it depends on your room temperature).
Bake at 180 degrees Celsius (325 degrees Fahrenheit) for about 30-45 minutes, or until the bread sounds hollow when tapped.
MORE ON BRIOCHE:
- Delicious Days makes saffron brioche 
- Brioche by Dorie Greenspan 
- "Rich Man's Brioche" with two cups (!!!) of butter 
- A photo step-by-step guide  to brioche making