Leave room on the edge & don’t over-stuff it. Mix a bit of rice wine vinegar with tamari sauce. I prefer Tamari sauce over regular soy sauce, it just tastes better. Take your finger and put a little of the sauce on the edge of the nori roll (that you left) to roll it up.
You should drizzle your rice vinegar/sugar/salt/mirin reduction a little at a time while the rice is spread to cool. Drizzle a little, then fold. Repeat until your reduction is gone and continue to let your rice cool until ready to use.
Don't try to store leftover rice. It's a petri dish for bacteria that cause food poisoning.
In addition to the already mentioned I have seen the following:
Cooked Tuna in more western style sushi such as spicy tuna roll
Shirako (cod sperm sack) is also used cooked in gunkan
Seared fish some fish such as tuna and, in Japan especially salmon is often seared with a blow torch on the nigiri
A common misconception is that the fish needs ...