It's a jordan for a gundam.
You can probably rescale it to fit other kits, I lost the blender file but it's not hard to edit. I made it to connect to the foot on the Build Strike Gundam Full Package, I'm not a massive gunpla guy (I've got like 3 kits and 2 of them are MG Zakus) so I'm not sure if other kits will need different connections.
I just mirrored the model for the other shoe, not perfect but it does the job, fit can be a bit tight sometimes but it works.
The author remixed this model.
Filled the bottom of the shoe and added an appropriate scaled hole to attach to the Build Strike Gundam Full Package.