1: Do at least a 50% water change to the aquarium water (be sure the new water added in is within 3-5F of the current tank water temperature), and treat the water with Seachem Prime according to directions (Seachem Prime helps reduce stress, helps slime coating, and dechlorinates water).
2: Keep the water temp in the aquarium around 74-76F (I use an Aqueon heater), as this seems to be an ideal temperature for ranchu in general.
3: Add 1-TBSP of Aquarium Salt (I used the Jungle brand) per 8-10 gallons of water (aquarium salt reduces stress, provides electrolytes, and cleans.. it may also raise your pH so be sure to dose accordingly). Although it may not be necessary, I added in a pinch of aquarium salt everyday after this initial dose until my ranchu no longer showed signs of ich.
4: Turn off any aquarium lighting to reduce any stress caused by glare, etc as these fish have already undergone enough stress at this point.
5: Be sure to run an air diffuser in your aquarium (along with a 24/hr running filtration system) for at least several hours a day to insure the fish are getting plenty of oxygen in the water (this is very important if you are using any other water treatments to remedy your fish outside of what I have on this post), this is especially important for smaller aquariums and/or ones with a higher temperature.
I hope my ranchu ich remedy works for others just as well as it did for my ranchu, and be sure to do another 50% water change a few days after having done the first one as to reduce the risk of having ich spread, etc (just be sure the new water you're adding into your aquarium is in the ideal temperature range as I mentioned before, too drastic a change may only worsen or cause the ich to reoccur). Good/adequate water quality can solve a lot of problems (be sure ammonia levels are also in a safe range, preferably no traces of ammonia, this is especially important if you have a small or overcrowded aquarium).