Cook rice however you normally prepare it.

While the rice is cooking, prep the tofu. In a bowl, mix the soy sauce, sesame oil, and sugar until combined. Pour the mixture into a non-stick skillet over medium heat. Add in the cubed firm tofu and toss gently until all the tofu is warmed through and evenly coated (~2 minutes). Turn off the heat and add in the sliced onion. Toss until evenly coated and set aside to cool.

Make the sriracha aioli by mixing the mayonnaise, sriracha, 1 tsp sugar, and squeeze of lime juice in a bowl, then set aside. Prep the rest of your toppings and set aside.

Once the rice is done cooking, transfer it into another bowl and while the rice is still hot, immediately add the rice vinegar, 5 tsp sugar, and 1 tsp salt by spreading evenly over the surface. Fold and mix the rice until all the rice is evenly coated. Keep folding and the rice will absorb the mixture while cooling down. Stop when rice is back to the original consistency. If the bowls are not ready to assemble yet, put a damp cloth or paper towel over the rice bowl so that the top layer doesn't harden.

Assemble the bowls with toppings of your choice!