I make a visual novel. And I had a problem. How to make a character appearance animation whose texture consists of various parts?
Use a RenderTarget. Render the character’s parts to a RenderTarget, and then apply that RenderTarget to a simple quad or sprite. Use that quad or sprite for your actual display. This approach has the added bonus of only needing to update the RenderTarget when the character changes in some way. So if your character is ever static, you can save on performance by not rendering every frame.
With your character drawn to a RenderTarget, you can adjust the alpha value for the entire quad or sprite, instead of the settings for individual pieces of your character. If you know what you’re doing, you could even only have the RenderTarget solution visible when you’re fading in and out.