For the teriyaki sauce, mix together soy sauce, tsuyu, sake, sweet rice wine, and honey in a small pot. Add the garlic, ginger and bring the sauce to boil. Reduce the heat to low and simmer for 5 minutes. Discard the garlic and ginger; set aside.
Heat oil in a large heavy bottom skillet over med-high heat. Add the onion and cook until they are just softened, about 2-3 minutes. Transfer to another plate; set aside.
Add the pork belly to the hot skillet and let them sear for 2-3 minute, then turn to the other side and cook for another 1 minute.
Pour the sauce over pork belly and let the sauce bubble. Reduce the sauce until it thickens, about 2-3 minutes. Remove from the heat.
To serve, put individual serving amount of rice in each bowl, put onion over the rice and top with pork belly slices. Sprinkle chopped green onion and top with an egg yolk. Serve immediately.