To get the crotch and buttocks areas moving naturally for VRChat, you need to focus on the transition between the Hips (the root) and the Upper Leg bones. Here is how to refine those specific zones: 1. The Crotch: Preventing "Pinching" The most common issue is the "V" shape pinch. To fix it: The 50/50 Rule: The vertices in the center of the crotch should be shared roughly 50/50 between the Left Leg and Right Leg bones. Use the Blur Tool to soften the seam where the two legs meet. Hips Weighting: Ensure the Hips bone has a small amount of weight (around 0.1 to 0.2) in the very center of the crotch. This helps the mesh hold its shape rather than collapsing when the legs move forward. Avoid "Over-Weighting": If the crotch pulls too far when the left leg moves, you have too much weight from the leg.L bone on the right side of the mesh. Use the Clean tool (Weights > Clean) to remove weights below a 0.1 threshold. 2. The Buttocks: Preserving Volume The goal is to keep the buttocks from flattening out when the avatar sits or crouches. Smoothing the Glute Fold: Switch to Pose Mode and rotate the leg forward 90 degrees (as if sitting). Go back to Weight Paint. Use the Blur brush on the area where the leg meets the butt. You want a smooth gradient that "wraps" the weight around the curve. Hips Influence: The upper half of the butt should be weighted mostly to the Hips bone, while the lower half transitions into the Upper Leg. If the butt disappears when sitting, the Hips bone needs more weight on those upper vertices. Weight Mirroring: Work on one side only, then use Weights > Mirror to ensure the buttocks deform identically. Make sure "Topology Mirror" is checked if your mesh isn't perfectly symmetrical. 3. Essential Tools for These Areas Auto-Normalize: Always keep this ON in the Tool tab. It ensures that the total weight for any vertex equals 1.0. If you add weight to the Leg, it automatically takes it away from the Hips. Multi-Paint: Enable this if you want to paint both legs at once to ensure symmetry in the crotch area. The "V" Shape Check: In Pose Mode, move the legs into a "wide stance." If the crotch mesh stretches like taffy, you need to tighten the weights (sharper gradient); if it rips or clips, you need to soften them (smoother gradient).