We usually make this in larger batches with the same 5:3:1:1 ratio and keep in the fridge for up to 2 weeks
Place all of the ingredients in a heavy pot. This can easily boil over and create a nasty sticky mess that takes forever to clean up. Or so I've heard.
Turn the heat on medium and keeping a careful eye on the sauce, reduce until the consistency of a very loose caramel
In Japan, teriyaki is usually fish and if you can get a hold of buri (Japanese amberjack) this is the way to go for sure.
In the US, it's generally easier to find chicken thighs and for this I prefer boneless and skinless. Season the chicken thighs with garlic powder, onion powder and pepper (but no salt). Poke full of holes with a fork and grill until about half done. Dip in the sauce and grill over medium to low heat until cooked through. Re-dip every 2 minutes or so. This burns easily so keep half the grill hot and the other lower temp.