Is it harmful if I run a tank of 100 octane in me 13 maxima?

 

For some more HP why not, I use to do this in my old Integra back in the days lol...never had A problem.

 

I personally have not seen any 100 octane UNLEADED fuel, but ...
1. If it is leaded fuel, yep. You will have issues down the road.
2. Running higher octane than your car has been engineered for really doesnt do more than take money out of your pocket. .

I would advise against it but if it was the only fuel available would get just enough to get me to the next gas station with mid grade.