This is a beginner level tutorial on how to create material morphs in order to make parts of a model disappear.
PMXE, that's all
If you've downloaded a R18 model, chances are that it already comes with morphs to remove all those annoying clothes. To verify if that's the case, load your model into MMD, select it and then check the facial manipulation box at the bottom.
Morphs are organized in 4 categories, the strip morphs are usually located under other, so test each morph one by one by pulling the slider to the right and pay attention if anything changes on your viewport. If the morphs are named Null_xx like the picture above, it means they're missing their english names, it's a minor annoyance and you can easily rename them in PMXE.
To make it simple, materials morphs are used to change the settings applied to the texture of a part of the model. We're going to use those to change textures from opaque to transpararent. Let's get started.
Open PMXE and load your model.
On your main view window, click the M button at the top to open the Refine/Masking window.
The Refine/Masking tool is used for isolating parts of the model and we will use it to check the names and numbers of the parts we want to make transparent.
To do so, start unticking and ticking each box until you find the ones corresponding to the clothes you want to remove.
In our case, we're going to make the entire dress disappear and it's composed of multiple parts.
Make a mental note of the names or numbers of each part then move to the main PMXE window (the scary one with all the tabs) then click the Material tab.
In this tab you'll find the same parts you found in the Refine/Masking window, select the ones you remembered from the previous step.
To the right are all the settings related to the texture, and as you can see, there's a 1 next to Opaque which means the surface is fully opaque.
If you set it to 0, the surface will become transparent (you have to set the Edge(Outline) A box to 0 as well so the outline isn't rendered) but that won't do, we can't have your model be naked all the time, we want to create an easily accessible slider to change the surface from opaque to transparent, from 1 to 0. So set everything back to their original values.
In order to tell our future morph which parts they should affect, we'll need to copy their reference first, so right click your selected parts then click Copy Index (X).
Now let's move from the Material tab to the Morph tab which uses a similar interface with the list of morphs on the left and their settings on the right. Those are all the morphs that you could find in the facial manipulation box shown in the introduction, we're going to create a new morph.
Right click anywhere on the list then select New (N) > Material (M)
This creates a new material morph at the bottom of the list, go check it out.
As you can see, the box on the right is completely empty, that's where we're going to paste the references we copied from the material tab so the morph understands which parts we want to work with.
Do so by right clicking the empty box and selecting Paste From Index (V)
The references will appear inside the box and we're now ready to modify their settings.
Select them all and click the Edit button on the bottom right next to Material Morph.
The window that opens uses simple maths to change the settings applied to the texture. By default it's set to Multiply at the top, meaning the original value of a settings is multiplied by the amount we set in this window.
Since the original Opacity value in the Material tab was 1 and we want to it be 0 to make the clothes disappear, we put a 0 in the Opacity box.
1 (original value) x 0 (multiply value) = 0 (final morph value)
We also want the Reflection and Outline to be 0 but a quick way to set everything to 0 is to click the "All 0" Button at the top then click OK.
We're basically done, our morph should be functional, we're going to test it.
Go back to your main view window, click the T at the top to open the Transform window.
In the bottom right is the list of all the morphs, scroll down to the bottom to find your newly created morph, select it.
On the right of it is a slider with 0 and 1 buttons below, either push the slider to the right of click the 1 button to activate the morph. The clothes should disappear. Congratulations.
Now before you leave PMXE (also don't forget to save), go back to your Morph tab and at the top is a box called Mrph Name, that's where you change the morph name so call it whatever you want, the two buttons to the right of it let you switch between japanese and english names, be sure to fill the english name box as well otherwise your morph will be called Null in MMD.
You can also use the arrow icons at the bottom of the list to reorder the morph and put yours higher in the list.
Now save your model and test it out in MMD.