VRoid Studio is an application for making (mostly anime-style) virtual avatars. Avatars are saved as .vmd files that can be used with programs such as VRChat, Unity3D, Blender, MikuMikuDance, and various VMD and VTuber software.
You create an avatar using the built-in body and clothing models, all of which have parametric options and can be retextured by importing texture files and by drawing on the model or texture view in-app. Each model contains a stack of textures that are overlaid to create a composed texture for the model. For example, an underwear texture may be overlaid over a tattoo texture, which is then overlaid over a base skin texture.