VRM4U is a comprehensive Unreal Engine plugin (UE4/UE5) for importing, rigging, and animating VRM (Virtual Reality Model) avatars. It provides both editor-time import workflows and runtime components for real-time character rendering and animation. The plugin supports VRM 0.x and VRM 1.0 specifications, along with related formats like GLTF/GLB, BVH, PMX, and VRMA. Core features include: skeletal mesh generation with humanoid bone mapping, MToon/PBR material conversion, morph target (blend shape) import with ARKit and MetaHuman mappings, spring bone physics simulation, ControlRig generation, and motion capture integration (VMC protocol, Sony mocopi, Oculus hand tracking). The codebase is organized into multiple UE modules (VRM4U, VRM4ULoader, VRM4UImporter, VRM4URender, VRM4UCapture) and includes both C++ anim nodes and Blueprint/Python automation scripts. The architecture follows a standard UE plugin pattern with editor and runtime separation. The import pipeline (VRM4UImporterFactory + VRMConverter) uses the bundled Assimp library for model parsing and RapidJSON for VRM metadata extraction, then procedurally creates UE assets (skeletal meshes, physics assets, animation blueprints, control rigs). The runtime module provides custom animation nodes for spring bones, constraints, VMC, and retargeting, along with a scene view extension for rim-light post-processing and GBuffer capture. The plugin also exposes a Blueprint function library for high-level avatar control (morph targets, material overrides, camera followers). Despite its depth, the codebase shows signs of maintenance burden: extensive #if UE_VERSION_OLDER_THAN guards for supporting UE 4.20 through 5.8, reliance on private engine rendering headers, and monolithic conversion functions. The bundled third-party dependencies (Assimp, RapidJSON) are fixed versions that require manual updates. However, the plugin is actively developed with frequent commits and broad feature coverage, making it a valuable resource for UE developers integrating VRM avatars.