I decided to re-create Eriksonix’s OC Emi in Koikatsu, but there was no way to add a custom texture to her mask, so I made one myself. The mod requires the latest KK_HF_Patch and the mod file to work. I hope you find this useful if not as an item you would use, then perhaps as an educational item into mod creation. Feel free to share, re-use, re-texture, etc.
Instructions: Download the .zipmod and place it into your mods folder in your Koikatsu folder. Put the character card into UserData/chara/female