Finished this quick weekend project:
https://github.com/hurui200320/GuliKitAPG

Some simple proprietary file format "reverse engineering" (I would say try and guess in plain English).

I thought it can replace an ESP 32 in Splatoon auto drawing, but the limitation is too bad. However, if you don't really need an ESP 32 and are willing to worst thing in automation, aka repeatedly reloading the controller, this might work. At least it's a controller, you can still play games with it. For an ESP 32 with normal people who don't want to step into this developing, it's just another E-waste.