This is a Fuji nut:
Yamaha use them on the rear axle of all the 700s (MT-07/XSR700/R7 etc) and possibly the MT-09 range too.
It acts like a Nyloc nut by way of that thin plate you can see at the top of the nut in the picture. I don't know why they use it although it is half the size of the axle nut on the SV and doesn't require any external locking but the SV has a plain nut and it isn't locked at all. Torque on both bikes are approximately the same at 105Nm (give or take).
There is a problem. The nut is supposed to be reusable and it is - providing the nut hasn't been seated for a while and/or the thin metal plate hasn't got dirty, then it gets interesting because it unscrews about 2 turns and then seizes. If you keep turning it carefully mangles the thread on the axle which is £70 (Fowlers say it has to be ordered from Japan).
I read about this soon after buying my XSR so I replaced it with a nut from Pro-Bolt but my friend with an MT-07 wasn't so lucky and needed a replacement axle when he replaced his chain (but found one at a breakers yard - £25). He's now bought a nut from Pro-Bolt too.
The nut sits in a recess/chain alignment guide so you can't cut off a bad nut before it destroys your axle.
Not one of Yamaha's better ideas imho.