(Using Blender 4.4.3 with the MMD Tools addon)
I’m trying to get some rigid body simulations to work, specifically some hair on this model of Yor that I have. I don’t know why the sides of her hair are breaking like this. Especially since her earrings are working perfectly fine.
I’m not sure if this is a problem with the rig as originally constructed or if something broke during the importing/physics appending process. For reference, here’s the rigid bodies themselves:
Oh, and here’s the blend file for troubleshooting. It requires the MMD Tools addon in order to get the idea of the issue I’m having.
Use the Goo Physics addon. It’s specifically designed for exactly this and it works much better than rigidbody
I don’t have GooEngine/Physics though, and my GPU card wouldn’t be able to run it anyway as it’s woefully outdated and underpowered. Plus I’d need to be a Patreon to Dylan in order to get that and money’s not something I have right now.
Couldn’t tell you. I haven’t used 3.6 in ages. Could be incompatibility with the add-on between versions or something along those lines..
UPDATE: So I tried opening the model in 3.6, result’s still the same. So I’m stuck with either 4.4’s brokenness or animating the hair with keyframe animation, something I don’t want to do.
And for proof:
I genuinely don’t know if it’s my computer/copy of Blender (regardless of version) being fussy with how MMD models are imported, or the model itself is corrupted. Because it works fine in its native program.
That’s weird.. becaus as i showed: it does work on my 3.6 
IDK if the “original” MMD rigid body settings were done in < 4.4 so they do not work properly in 4.4..
Maybe you have touched other bones that may affect the hair?
I opened the file in blender 4.5.8 LTS, pressed play and it looks good.
I installed MMD Tools and the animation looks the same.
However, if I bend the back using one of the other spine bones, the hair gets mangled as in your image. It’s as if the physics needs to be recalculated.
So, I clicked the Physics button, reset the animation to the start frame and clicked the button again.
And now the hair looks good.
N.B., I just have 5 minutes of experience with MMD Tools, so I don’t really know what the button does.
Wiggle bones is free and might work? https://extensions.blender.org/add-ons/wiggle-bones/
