>>274566412
https://www.youtube.com/watch?v=_jTeVbH5D4c
Do this, then follow standard steps for MMD models. You're gonna have a lot of bones so just parent the ones you don't need. Keep the eye bones though. Make sure you name all the shapekeys to the same thing when joining so they all flex together (or don't if you want more freedom, but blinking is gonna be weird).