That's a good question, but I'm afraid it works the same as the previous example, meaning that the power of the fire is divided amongst them.To begin the next technique I begin to mold my spiritual and physical energy once again allowing them to mold together to form raw chakra. Once completed I then use the chakra and heat it up within my lungs creating katon chakra enabling the use for this technique. I quickly reach down to the ninja tools pouch strapped to my leg under my cloak and throw two shuriken out. Once the shuriken are flying I expel my fire chakra to the shurikens, infusing them with fire. Then by my command I unleash the infused fire and ignite the shurikens.
The first and most obvious advantage to this technique is that you give your shuriken an extra punch over the regular shuriken. The fire infused shuriken will become stronger in enemy wind techniques given that the wind technique isn't B-Rank or above. The technique is also chakra efficient give the quantity of shuriken you can produce.
I do have one question regarding the quantity. So if you use one shuriken and infuse it with fire it will be D-Rank? And if you use two each of them will be E-rank? Or is it independent from this jutsu since they are shuriken that are just infused with fire? Just need some clarification there
There are a few disadvantages to this technique. Namely that it would only take a low level suiton jutsu to block these easily. As well as other shuriken or kunai to block them in mid air. The katon chakra doesn't actually add any cutting power or speed to any other shuriken and kunai can easily just intercept them.
To use it offensively as you said I could take advantage if my enemy uses a fuuton against me. This way the shuriken will gain strength in the fuuton and create a larger fire. However if I do this I will also still need to defend against the incoming fuuton as the shape and size of the shuriken will not neutralize it. I could also use my own fuuton in conjunction with it to give it strength. The shuriken can also be used as a good distraction to bait the opponent to possibly using one of their three jutsu per turn to put them at a slight disadvantage.
To defend against it as I said above I could throw my own shuriken and kunai. If this isn't possible in some circumstances I could use suiton to block the shuriken and extinguish the infusion of fire.
Yes, the best defense would be to focus on the shuriken and ignore the fire. Why? Because the shuriken are the medium that carries the fire and if you deal with the medium, you've dealt with the fire as well. What that means, anything that has great mass like a wave of water or an earthen slab could stop the shuriken. Wind would work as well but you would need a B rank technique, at least. However, a B rank wind would not only stop the shuriken and blow away the fire, but it could also potentially return the shuriken back to the owner, which is a win-win situation for you.