Shape rice into eight small patties by pressing firmly into a 3-inch mold or your hands.

Heat 1 tablespoon sesame oil in a large nonstick skillet over medium-high heat. Add rice cakes and cook for 4–5 minutes per side until golden and crisp. Transfer to a plate.

In the same skillet, add remaining sesame oil. Sear chicken pieces in batches until browned, about 3 minutes per side. Remove and set aside.

Whisk soy sauce, mirin, sake, brown sugar, ginger, and garlic in a bowl. Pour into the skillet and bring to a simmer.

Return chicken to the skillet; cook until sauce thickens slightly, about 3 minutes. Stir in cornstarch slurry and cook 1 minute more to glaze.

Arrange crispy rice cakes on a serving platter. Spoon glazed chicken over each cake. Garnish with green onions and sesame seeds.