CustomSteve

CustomSteve is a mod that allows users to substitute default Minecraft player model with industry-standard model, most notably 3D models used by MikuMikuDance (abbr. MMD).

Demo
Several demonstration pictures and videos are available in the original post. Here are links for part of them:
 * https://www.youtube.com/watch?v=rGltAWLIEJw (may be blocked due to legal reason)
 * https://www.youtube.com/watch?v=zcWAIsZ2PV0

CustomBuki
CustomBuki, according to author's introduction, is a sub-mod of CustomSteve that provides a fully customizable weapon system alongside with 3D model format support. Buki in the mod name is Japanese romaji for "weapons" or "arms". Currently this mod is still a work-in-progress, and only few videos are available so far, for example, a demo made by ici2cc.