Freeze extra firm tofu overnight. Thaw on the counter for a few hours or microwave for 2 minutes.
Squeeze the extra water out and dap with paper towels to ensure there's no moisture.
Make your marinade - combine soy sauce, mirin, sake, and brown sugar. Give it a good stir.
Break your tofu into chunks and add to the marinade. Toss it until fully coated and marinate for about 20 minutes.
Soak your bamboo or wooden sticks in water. This is to prevent them from burning when you are grilling them.
Meanwhile, chop your desired vegetables like green bell pepper into 1cmx1cm chunks or squares.
Insert them one by one - tofu followed by green bell pepper and repeat until your stick is 3/4 full.
Add some oil to a flat frying pan. Lay down your skewers and flip them once they are grilled and slightly charred. Drizzle with more of the marinade as they are frying.
Once done, sprinkle some marinade and nori flakes on your rice. Place the skewers on top and top with sesame seeds. Enjoy!