This mod is intended as a base for mod creators who want to use hair physics on their custom models that replace Kiryu and not Majima.
It covers most of Kiryu's models.

Main files do not require Ryu Mod Manager but they are compatible with it.
Collision files require Ryu Mod Manager or manual .par repacking.

How to use:
Version 1 always loads Majima's ponytail for Kiryu, if you do want that for whatever reason.

Version 2 makes the game always load hair, but it's invisible, so you can't see the changes out of the box. This will allow you to handpick which Kiryu models you want to add hair physics on, without altering the other ones. Just replace the mesh.par corresponding to the model you want to edit. (for example: chara > w64 > accessory > b_c_cm_kiryu_hair1 > mesh.par for Kiryu's main gameplay model.) You can't outright delete these meshes or it will infinite load. If you want to disable the hair while this mod is enabled, just take one of the empty mesh.par given in version 2.

Your mesh.par for Kiryu's hair needs to be packed to work. No unpacked pars.

It will not work if you somehow managed to rename Kiryu's model folders, but if you succeeded in doing that you know how to make it work.

Optional files: Adds collision to Kiryu's models for the ponytail not to clip through him. Compatible with custom models.

How to make your own custom hair physics mesh (for knowledgeable Blender users):

Import Majima's original ponytail (chara > w64 > accessory) into Blender with Theturboturnip's tool. Look at the way it's weight painted and try to do something similar on your own mesh for optimal physics. You can not edit the bones. Do not weight paint physics higher than where Majima's ponytail starts. If it's higher, paint the high part to face_c_n or the physics will float (I'm trying to find a solution for that, if you find one please tell me). Replace the hair mesh of whatever model you want. Obviously make the body mesh bald.
Sadly collision will only work for the higher part of the body, meaning longer hair can have physics but will clip through your model's body.
Collision can also fuck with hair meshes that are too different than Majima's so try disabling the collision it if it looks weird. (collision is determined by the .hcb files, they can be deleted)

I couldn't test every single model so please report to me any issues. Feel free to DM me for help or if you want to add hair physics to a model not included here.

(discord: Eve ?#0001)

Kiryu models not supported yet:

c_at_kiryu_d_01_020_b_hand
c_at_kiryu_naked_17_120
c_at_kiryu_naked_17_120_bd
c_at_kiryu_naked_houtai
c_at_kiryu_origin_shirt
c_cm_kiryu_naked_c14_care
c_cm_kiryu_hair_reduct_A
c_cm_kiryu_hair_reduct_B

Huge thanks to ♡Max♡ for calculating my checksums!

Ponytail for Majima Origin by bihuraj00