- Heat olive oil over medium-high heat for 2 minutes in a large skillet. Blot beef with paper towel to remove excess moisture and season on all sides with salt and pepper. Sear beef for 6-8 minutes, turning frequently for even browning.
- Transfer beef to slow cooker. Stir together Takumi and 1 cup of beef stock in a large measuring cup. Pour over beef. Cook on high for 4 hours or low for 6-8 hours.
- Slice or shred beef on a cutting board. If sauce needs thickening, whisk together cornstarch and remaining half cup of beef stock and stir into crockpot. Add beef, cover and cook 30 minutes longer.
- Serve hot garnished with chopped green onion.