Nevus of Ota hasn't faded after 13 sessions. Should I try something else? (photo)

You did not specify what the 13 sessions of treatment were. However, as this melanocytosis lies within the upper third of the dermis, Picoway treatment most likely is the best treatment option. You could use the resolve handpieces of the 532 and 1064 wavelengths along with the Zoom treatment with the 730 wavelength handpiece as a spot treatment with low energy settings. Of course with safety first ,it will take multiple sessions 8-10 weeks apart.