They allow characters to react more naturally to light sources within a scene, reducing the "plastic" look of skin and hair.

Xukmi’s FX shaders introduce several critical features that were previously missing or limited:

Xukmi FX Shaders (specifically [xukmi][KK] xukmi FX Shaders v1.0.zipmod ) is a popular visual enhancement mod for the game

Choose the section that fits your need.

xukmi/KKShadersPlus: Recreated Koikatsu shaders ... - GitHub

If is your own project, feel free to use or adapt this content. If you need help with actual shader code ( .vsh , .fsh , composite, or pipeline setup), let me know and I can provide GLSL examples or troubleshooting steps.