A standard 12mm combination wrench has squeaked by for me in the past. Using the open ended end..
But these wrenches (which can be found anywhere) are short, and the box end is always angled, which won't fit in that tight gap. If you use one of these wrenches and manage to get the nuts off without completely rounding off the corners, replace the nuts with new Toyota ones... so you can get them off the next time. Each time you use this wrench on these nuts, the nut's hex corners get rounded off a little more......
The Toyota PN for those nuts is:
90179-08123
If the wrench shown above doesn't work. The
wrench below is the cat's meow for the fan clutch nuts.
Snap-On Wrench, Metric, Hi-Performance, Box, 0° Offset, 12-13 mm, 12-Point
Stock#: XDHFM1213
This wrench is long, so it's easy to get down in there, and the box is not offset so it can be inserted straight down in that tight gap. You just need to file the thickness of the box a tad with a hand file so it fits in the gap...
This wrench makes removing the fan clutch nuts actually fun... But it is very expensive. Ebay deals can be cheaper if you can find one.