So here’s a low poly body I made just like how I modeled Azusa. The difference was, instead of extruding her arms from her body, I made her arm from a separate cylinder.
Her arm was made from a cylinder with 8 sides and shaped by adding edge loops as below.
Four faces on the side of her body was selected (since that makes 8 sides)…
and extruded inwards to make the ‘octagon’ smaller and shaped more round.
After the body mesh and the arm mesh was combined (by selecting two meshes and firing off Mesh => Combine) and unwanted faces were deleted, the arm was attached to the body by selecting pairs of vertices (1 from the arm and 1 from the torso) and firing off Edit Mesh => Merge to Center eight times.
So it’s easy enough attaching limbs if both sides had the same amount of vertices to connect. But the hand that I wanted to attach had many more vertices than the wrist.
To solve this, the edge loop at the wrist end of the hand was extruded twice.
Then every second edge at the wrist were deleted.
Using the Split Polygon Tool, two triangles were made as below…
then the tris were made into a quads by making two new edges with the same tool like below.
The same was done all around the wrist.
I still had 12 vertices at the wrist of the hand mesh, and I wanted to pull that number down to 8. So I repeated the steps again by extruding the last edge loop out, deleting edges…
and making extra quads as below.
Now I had 8 verts at the end of the hand mesh and 8 verts at the wrist of the body mesh, so I could attach the hand to the wrist like I attached the arm to her shoulder.