Cut 1.75 pounds (800 g) boneless beef short ribs into 1-inch (2.5 cm) pieces. Season evenly with 1/2 teaspoon kosher salt and 1/8 teaspoon black pepper.
Turn the pressure cooker to the saute setting and heat 1 tablespoon toasted sesame oil.
Sear the beef in batches to avoid crowding the pot. Cook for 1 to 2 minutes per side until browned. Transfer the browned beef to a plate.
Pour 2 tablespoons of water into the pot. Scrape the bottom with a wooden spoon to release the browned bits.
Add 1 medium yellow onion, cut into wedges. Cook for 2 minutes. Stir in 2 cloves minced garlic and 1 inch (2.5 cm) sliced fresh ginger, cooking for 1 more minute.
Return the beef and any resting juices to the pot. Pour in 1/4 cup (60 ml) soy sauce, 1/4 cup (60 ml) mirin, 2 tablespoons sake, and 2 tablespoons brown sugar. Stir well.
Fold in 10 ounces (280 g) peeled and sliced daikon radish and 1 large peeled and chopped carrot.
Secure the lid and set the valve to sealing. Cook on high pressure for 35 minutes.
Let the pressure release naturally for 15 minutes, then carefully vent any remaining steam. The beef should be very tender and reach a safe internal temperature of at least 145°F (63°C). Garnish with 1 sliced green onion to serve.