Steps
1. Thinly slice the beef against the grain and set aside.
2. In a bowl, mix soy sauce, mirin, sake, brown sugar, garlic, and ginger to create the marinade.
3. Add the sliced beef to the marinade and let it sit for at least 15 minutes.
4. In a pan, heat sesame oil over medium-high heat. Add the marinated beef and cook until browned and cooked through, about 3-5 minutes.
5. Pour any remaining marinade into the pan and cook for an additional 1-2 minutes until the sauce thickens.
6. Serve the beef over a bowl of cooked rice and garnish with chopped green onions and sesame seeds.