While doing some Taoism research, I discovered incense is a way to communicate with the 12 Divine Generals.
That's how I learnt that the 12 Divine Generals are associated with the animal zodiac and that it's a very common idea in Eastern myth!
But, more on incense...
Ten has a post on the Tsuba Guard power.
Isn't that beautiful?
The 12 Tsuba Guards are the 12 divine general's powers. Incense is used to communicate with them.
So the Tsuba Guard gauge being incense fits perfectly because we need it to be 'full' in order to use the power of the generals! (We are offering incense to them)
Shinto has its roots in Taoism so they have much in common. That's why I wonder if the Shinto present in Kunitsu-Gami is closer to Taoism.
(I know it's correct english to write out 'twelve' but that's just for books, right? I prefer using 12.)