When I moved to New Mexico I learned some interesting things about peppers and chili peppers. One is that if you look closely at the power if there are any dark/black specs in it that’s ground up stem. So take a close look at your pepper. Look at the source or farmer and dig around until you find a great quality pepper.
Another fun fact I learned about peppers in general is that when you roast them you peel the crispy skin off instead of rinsing it. This preserves the flavors and add some from the skin.
For sushi the main thing chili pepper is used for is creating The Top Secret Ginger Tataki Sauce. Spicy Tuna or Salmon is another great way to mix in your favorite chili pepper.
It’s not really a traditional ingredient but it’s made its way into the sushi bar.