The game maps use this format; each level has a map divided into sections. I'll also send the textures to help with visualization. If anyone knows a way to edit or convert them, I would be grateful.

ST01-TEXTURE.zip ST01.zip

Looks simple. First you must parse vertex buffer, index buffer and then is table with info about shapes and textures.

//------------------------------------------------
//--- 010 Editor v14.0 Binary Template
//
//      File: Tenchu: Return from Darkness
//   Authors: 
//   Version: 
//   Purpose: 
//  Category: 
// File Type: *.bgm
//  ID Bytes: 
//   History: 
//------------------------------------------------
LittleEndian();OutputPaneClear();

local uint32 i,j,k,l,ElementBaseOffset,IndexBaseOffset;

FSeek(36);

uint32 TotalElementCount;
ElementBaseOffset=FTell();
byte Elements[TotalElementCount * 24];

uint32 TotalIndexCount;
IndexBaseOffset=FTell();
ushort Indices[TotalIndexCount];

struct
{
    uint32 ShapeIndex;
    
    struct
    {
        uint32 IndexOffset,IndexCount,ElementOffset,ElementCount;
        uint32 ShapeId;
        string TextureName;
        FSeek(startof(TextureName));
        FSkip(32);
        uint32 Unk4;
        float BBox[6];
    }Shape[ShapeIndex]<optimize=false>;
}Shapes;

FSeek(ElementBaseOffset);
struct
{
    for (i=0; i < Shapes.ShapeIndex; i++)
    {
        struct
        {
            FSeek(ElementBaseOffset + Shapes.Shape[i].ElementOffset * 24);
            struct
            {
                float VPosX,VPosY,VPosZ;
                ubyte R,G,B,A;
                float UVPosX,UVPosY;
            }Elements[Shapes.Shape[i].ElementCount]<optimize=false>;
            
            FSeek(IndexBaseOffset + Shapes.Shape[i].IndexOffset * 2);
            struct
            {
                uint16 Index;
            }Indices[Shapes.Shape[i].IndexCount]<optimize=false>;
        }ShapeBuffer;
    }
}ShapeBuffers;

from inc_noesis import *
import noesis
import rapi
import os

def registerNoesisTypes():
   handle = noesis.register("Tenchu: Return from Darkness - Mesh", ".bgm")
   noesis.setHandlerTypeCheck(handle, noepyCheckType)
   noesis.setHandlerLoadModel(handle, noepyLoadModel)
   noesis.logPopup()
   return 1
        
def noepyCheckType(data):
   bs = NoeBitStream(data)
   if len(data) < 20:
      return 0
   return 1
        
def noepyLoadModel(data, mdlList):
	bs = NoeBitStream(data)
	baseName = rapi.getExtensionlessName(rapi.getLocalFileName(rapi.getInputName()))
	ctx = rapi.rpgCreateContext()
	Underline = "_"

	CurPos = bs.tell()
	bs.read(20)
	Type = bs.readUInt()
	if Type == 1:
		bs.seek(CurPos, NOESEEK_ABS)
		bs.read(36)
	else:
		bs.seek(CurPos, NOESEEK_ABS)
    
	TotalElementCount = bs.readUInt()
	ElementBaseOffset = bs.tell();
	ElementBuffer = bs.read(TotalElementCount * 24)
	rapi.rpgBindPositionBufferOfs(ElementBuffer, noesis.RPGEODATA_FLOAT, 24, 0)
	rapi.rpgBindColorBufferOfs(ElementBuffer, noesis.RPGEODATA_UBYTE, 24, 12, 4)
	rapi.rpgBindUV1BufferOfs(ElementBuffer, noesis.RPGEODATA_FLOAT, 24, 16)
        
	TotalIndexCount = bs.readUInt()
	IndexBaseOffset = bs.tell();
	bs.read(TotalIndexCount * 2)
    
	ShapeIndex = bs.readUInt()
    
	for i in range(0, ShapeIndex):
	    IndexOffset = bs.readUInt() * 2
	    IndexCount = bs.readUInt()
	    ElementOffset = bs.readUInt() * 24
	    ElementCount = bs.readUInt()
	    ShapeId = bs.readUInt()
	    TNamePos = bs.tell()
	    TextureName = bs.readString()
	    bs.seek(TNamePos, NOESEEK_ABS)
	    bs.read(32)
	    Unknown = bs.readUInt()
	    BBox = bs.read(24)
	    cPos = bs.tell()
	    ShapeId = "{:04d}".format(ShapeId)
                            
	    rapi.rpgSetName(baseName + Underline + ShapeId)
	    rapi.rpgSetMaterial(TextureName)
	    if IndexCount != 0:
	        bs.seek(IndexBaseOffset + IndexOffset, NOESEEK_ABS)
	        IndexBuffer = bs.read(IndexCount * 2)
	        rapi.rpgCommitTriangles(IndexBuffer, noesis.RPGEODATA_USHORT, IndexCount, noesis.RPGEO_TRIANGLE_STRIP)
	    bs.seek(cPos, NOESEEK_ABS)
	mdl = rapi.rpgConstructModel()
	mdlList.append(mdl)
	return 1

Just drop the bgm into the texture folder named as the bgm. Noesis should open it with texture applied. Not sure when export tho. I set material name as texture name.

Vertex color works too.

Edited May 18May 18 by h3x3r