Live2D / VRM Character Animation

What does VRM Character Animation do?

This skill comes from a desktop pet that supports both Live2D and VRM characters (see "Source & Maintenance" at the end). Models used include official samples, VTube Studio models, and VRM models converted from VRChat. The approaches below have all been tested, measured, or reviewed by users.

Three Principles That Apply to Both Character Types

1. Procedural layers and animation clips overwrite each other. Which value is calculated first and written last per frame determines what the user sees. Almost all "snapping," "hand dropping," and "head not moving" issues originate here:
   • Live2D: Values procedurally overlaid inside beforeModelUpdate do not enter physics – hair and body will not follow. Wrap around physics.evaluate and overlay before physics.
   • VRM: When the three.js AnimationMixer blends values that are the same as the previous frame, it does not write to the bone. The procedural standing pose and breathing set each frame will leak through during motion clips that "hold" a pose. Skip bones that are being written by the currently playing clip (by node name from clip.tracks). The same applies when paused – stop the procedural re-write of the standing pose.
2. Do not modify the motion files; add a procedural layer on top. Hand-keyed and AI-generated motions often only move a few bones (a wave only moves the arm) and feel puppet-like. Add a procedural "follow-through" layer after the clip – shoulders rise with the arm, torso yields, wrist lags, head trails half a beat – without layering on bones already written by the clip. Do it once, and all motions benefit, with the ability to toggle for comparison.
3. Verify by frame-by-frame numerical logging, not by eye. Animation glitches last only one or two frames, making them nearly impossible to confirm visually. Log the value of the problematic bone (parameter) at the moment it is drawn (after render, or in Live2D's beforeModelUpdate), record it before and after the fix, then compare; also capture screenshots on two different models.

Where to Read What

Task	Reference
Live2D: loading, writing parameters, physics, idle, motion, hold, expressions	references/live2d.md
VRM: procedural poses vs. clips, follow-through, motion-capture clips, expressions, spring bones, transparent windows	references/vrm.md
VRM: motion + expression, hand shapes and wrist, hand-to-body IK, no hand drop on interrupt, leg limits, eyes follow head, keyframe interpolation and segmentation	references/vrm.md items 19–31
AI-generated or modified expressions and motions	references/ai-motion.md
Nod to music, head motion while speaking	references/live2d.md item 16, references/vrm.md "follow the beat"

Most Common Pitfalls (Check These First)

Symptom	Cause	Fix
Live2D reports "Could not find Cubism runtime" or fails to render	Wrong loading order	Cubism Core → register render pipe module → PixiJS Application.init() → model
Live2D parameter writes read 58, null, etc. strange values	String IDs passed directly	Convert to handle first with internalModel.getIdSafe(name)
Live2D head does not move (VTube Studio model)	ParamAngle* is physics output; written over	Read physics3.json, redirect writes to its input parameters
Live2D only head sways; hair and body don't follow	Overlay placed after physics	Wrap physics.evaluate and add overlay before it
Live2D stands completely still	VTube Studio model lacks a proper Idle animation	Programmatic idle: three slow sine waves on head + body + breathing, only write standard parameters
Live2D restarts moving after stopAllMotions	Engine starts playing Idle when no motion is playing	Point motionManager.groups.idle to a non-existent group, then stop breath
VRM hand-keyed motion: hand drops during held pose; snap at start/end	Mixer does not write unchanged values, procedural standing pose leaks through	Skip bones written by the clip when applying the procedural pose
VRM one-shot motion jumps back to standing pose at end	With clampWhenFinished=false, the mixer closes the action before finished fires	Set clampWhenFinished = true, then fadeOut
VRM motion-capture pose is too wide; legs shift at start; skirt flies up	Clip includes hip and leg tracks	Delete hip and leg tracks during conversion; use only upper body
VRM skirt clips through thighs; collider helper shows only one or two spheres	Colliders not registered in the spring chain's collision group (three-vrm only recognizes registered ones)	Add leg capsules to the chain under the hip using standard bones; do not jump the hip in one frame (references/vrm.md item 15)
VRM expressions in the clip are invisible	Per-frame state expression, blink, and lip-sync overwrite them	Write only bones in the clip
Expression invisible at small screen size	Expression file only changes a small area	Add a layer of parameters per emotion (squint, blush, tilt, mouth corner)
VRM motion has no facial expression	Expression only follows state, not motion	Write mood + beats alongside the motion, blend by motion weight (references/vrm.md item 25)
Motion requires closed eyes, open mouth, but model's "sleepy" or "smile" blocks it	Expression's overrideBlink / overrideMouth block it	Suppress those expressions during the motion (item 26)
VRM single-eye blink invisible	blinkLeft/blinkRight not bound to morph targets	Squint both eyes together instead (item 27)
VRM one motion interrupts another; hand drops then raises	New motion starts from standing pose; crossfade passes through standing pose	Start from the most similar pose in the new motion + transition from the interruption point (item 19)
VRM motion-capture fingers: flat or clenched; hand-keyed fingers half-closed	Retargeted fingers / motion does not write fingers	Remove captured finger data; write hand shapes in the motion (items 22, 23)
Hand-to-chin, hand-over-mouth, heart shape miss the target when model changes shape	Only angles written	Calculate target per bone and mesh in real-time; two-joint IK (item 24)
Dance ends; leg snaps back in one frame	Leg IK takes over instantly when fade-out begins	Gradually transition IK weight based on the leg motion weight (item 20)
Knee semi-bent; relaxed leg bends too much	Multiple hip offsets stack together	Apply knee limit; halve hip compression; lifting heel increases bend (item 21)
VRM eyes always stare at camera	lookAt targets camera; eyes rotate opposite to head turn	When head turns, eyes follow head, blink during turn, micro saccades (item 28)
Hand-keyed motion jerky / discontinuous	Each keyframe segment slows at both ends; each keyframe velocity is 0	Monotone cubic spline + stagger keyframes across segments (item 29)
Stretch / raise arms: arms sweep up from sides at 90° / extend sideways	No fist-pull, forearm-fold segments; twist and raise not separated	Segment and rebuild; twist only at the door frame moment (item 30)
Idle weight shift: upper body tilts entirely to one side	Knee limit reduces hip lean; waist and chest still rotate fully in opposite direction	Add the reduced hip lean amount to the waist (item 31)

Source & Maintenance

• Source: Cirra (AI desktop pet, RedCarpG/cirra-deskpet), October 2026 to November 2026.
  • Live2D code: src/pet/live2d.ts, src/pet/live2d-physics.ts, src/pet/cubism-core.ts; rendering library untitled-pixi-live2d-engine 1.4.0 (PixiJS 8).
  • VRM code: src/pet/vrm.ts, src/pet/vrm-motion.ts, plus vrm-face.ts, vrm-hands.ts, vrm-blend.ts, vrm-reach.ts, vrm-gaze.ts from 2026-11-11; commits 2b6ab57 (clampWhenFinished), e5e8687 (no combineSkeletons).
  • Documentation: docs/stage5.md, docs/live2d-motions.md, docs/live2d-common-motions.md, docs/live2d-studio.md, docs/loop-motions.md, docs/expression-outfit-split.md, docs/music.md, docs/vrm.md, docs/vrm-motion.md, docs/vrm-motion-library.md, docs/vrm-studio.md, docs/vrm-toon.md, docs/beat-tracking.md, docs/vrm-skirt.md, docs/vrm-motion-polish.md.
  • Experience: Private repo lessons/live2d-motion.md, lessons/threejs-vrm-animation.md.
• Upstream: skills/live2d-vrm-animation/ in RedCarpG/redcarpg-skills. The copy under ~/.claude/skills/ is an installed copy and should not be edited directly. The code in Cirra is its source; the two are not automatically synchronized.
• How to modify:
  • Edit in redcarpg-skills via PR; increment version in manifest.json, pass node scripts/validate.mjs, then tag (live2d-vrm-animation-v<version>) and reinstall the local copy. First check the two lesson files above for new items that could be included.
  • After upgrading three.js, three-vrm, or the Live2D rendering library, re-verify the entries in the "Most Common Pitfalls" table that relate to internal library behavior (mixer not writing unchanged values, clampWhenFinished, shouldRequestIdleMotion, loading order).
  • If a symptom is observed on only one model type, indicate which model type; do not generalize.
• Changelog:
  • 2026-11-12 · 1.0.0, moved to redcarpg-skills for public release. Removed local absolute paths, linked to source project; content unchanged.
  • 2026-11-10 · Cirra · Initial version: three principles, pitfall quick reference; Live2D, VRM, AI-generated motion references; two test prompts in evals/.
  • 2026-11-10 · Cirra · Revised VRM item 15 (skirt clipping): original "just use capsules" fix didn't work; replaced with collider group registration, generic leg capsules, and hip-jump avoidance (docs/vrm-skirt.md); added row to pitfall table.
  • 2026-11-10 · Cirra · Item 15: added long hair into sleeves (arm capsules cannot be retracted); clothing bulging out is a skinning issue.
  • 2026-11-10 · Cirra · Added to references/vrm.md: "Standard bone VRM 0.x faces -Z" (change orientation for procedural poses; don't cancel out rotateVRM0 when turning; commit e2e6c0c, src/pet/vrm-basis.ts).
  • 2026-11-11 · Cirra · Added items 19–28 to references/vrm.md (no hand drop on interrupt, IK takeover during leg clip fade-out, knee limit and heel lift, retarget captured fingers to hand shapes, hand shapes and wrist, hand-to-body IK, motion expression pairs, override blocking beats, empty single-eye blink, eyes follow head); updated item 11 to point to item 25; added face, hands, reach format and validation to ai-motion.md; added 9 rows to pitfall table. Source: docs/vrm-motion-polish.md §10, §11, src/pet/vrm-face.ts, vrm-hands.ts, vrm-blend.ts, vrm-reach.ts, vrm-gaze.ts, vrm-clip-extras.ts, vrm-pose.ts, sidecar/src/shared/motion-face.ts, motion-hands.ts (merged commits b2f115d, ea3be9e).
  • 2026-11-11 · Cirra · Added items 29–31 to references/vrm.md (keyframe per-segment deceleration causing jerkiness → monotone cubic spline and staggered keyframes; stretch/segmentation and upper arm twist; knee limit reducing hip lean causing upper body tilt); added 3 rows to pitfall table. Source: docs/vrm-motion-polish.md §12, src/vrm-studio/motion-spec.ts smoothAt, src/pet/vrm-pose.ts (merged commit c5b4728).
  • 2026-11-11 · Cirra · Added to references/live2d.md item 21: two exclusion categories for VTube Studio models (physics inputs, non-Param facial parameters) to prevent facial expression from yielding during nodding. Source: src/pet/clash.ts standardInputs, isStandardParam, docs/expression-clash.md (commit 7721742).