Basically, the file that you can download up there comes with 3 files.
FIRST you throw in the Main unity package thats called "DanmenShaderKitForVRC_v1.0.0", which isnt the full thing, its more like a joke item.
THEN there is another unity package that needs to be installed, which is called "DanmenShaderKit_ExTex01_v1.0.0", which replaces the textures to the lewd XRAY that it shows in the main thumbnails of the Asset.
Once you have installed both packages in order as I described, open up the new folder that appears in your assets on unity and look for the "DANMENforVRC" prefab, in which you will drag and drop onto your avatar and it has a Bone Proxy component that will attach to your hips.

It uses its own SPS, but you can set it up to use another SPS on your own avatar if you know how to (I didn't want to bother changing it so Its best to leave it alone if you dont to mess it up)

If you want to move the SPS, look in the hierarchy and go to DANMENforVRC->HipsBone->SPS Socket
If you want to move or scale the XRAY itself, look in the hierarchy and go to DANMENforVRC->HipsBone->Danmen

Its kinda weird that the textures are seperated from unity packages.
TLDR; it works as a lewd XRay for ERP, however you don't actually see your own PP when you or someone else inserting, its actually just a Animation of a PP going in and out of a womb that syncs up with a SPS PP, like how you use a Slider in a VRC menu to scale boobs bigger or smaller, but its controlled by a SPS PP
Its still really good though, I recommend it, very hot and sexy.

I guess this will serve as a guide for others who are somehow having problems or are confused.

Translated from Japanese from their product page:

Everyone's favorite cross-section diagram is finally here!

You can use it for taking photos and videos in Unity, as well as other fun stuff!

It includes a prefab with a ModulerAvatar and VRCFury (SPS) settings, making it easy to set up.

It also includes a HUD, tablet, and sound effects for even more fun.

*This product is a joke item and was created with the intention of being enjoyed in the Unity editor.