Since this is an expansion set, it doesn't form a complete unit on its own.
The most essential parts are shown above.

The drum frame at the bottom of the claw/thruster unit slides out with a wide range of motion.

There are times when you need to lock it at an intermediate position,
but there's a stopper inside that holds it there nicely.

The beam emitter open gimmick on the right claw unit..

When attaching the sub-arm to the drum frame,
there are cross-shaped pegs that lock it at 90-degree intervals on the fixing pin.
In other words, once you push it in all the way it won't rotate — this is a mechanism to prevent it from drooping down under its own weight.

The reinforced winch cannon opens by removing the cover and repositioning it elsewhere.

The articulation at the tip of the reinforced winch cannon.
This part tends to pop off during posing.

One leftover part remains due to duplicate runners.

The HGUC Hrairoo released in 2006 does include some parts of the Hrududu II as well. (left)
It comes with two claw/thruster units and one sub-arm — let's compare them with the HGUC Hrududu II Expansion Set.

First, the movement mechanism of the drum frame at the bottom of the claw/thruster unit is different.
The HGUC Hrairoo uses a detach-and-reattach system, while the HGUC Hrududu II Expansion Set has evolved to use a slide mechanism.

The beam emitter open gimmick is pretty much identical.

The HGUC Hrududu II's drum frame is symmetrical and can be connected freely on either side,
whereas the HGUC Hrairoo version (on the left) has different left and right shapes.

The overall shape of the sub-arm is pretty much the same.

But the sculpting of the claw section and the parts configuration are different.

Also, the HGUC Hrududu II has locking pegs on the sub-arm connection pin, which is another difference.

To build a complete Hrududu II, you'll need to borrow from the HGUC Hazel II
the lower body (drum frame + Booster pod) and composite shield.

Joint parts needed to assemble the Hrududu II main body

You can build the Hrududu II using the layout and configuration shown above.

First, fix the cockpit block to the upper waist section of the Hazel II's lower body,
then deploy the weapon mount below the crotch area.

Add two joint parts at the bottom to set the angle.

Curl the Hrududu II main parts into a ring shape as shown and firmly connect the ends,

then add separate joint parts on the inside and attach them to both sides of the main body to complete the combination.

For the stand, the instructions recommend borrowing an Action Base 4 — the kind sometimes included with Figure-rise Standard kits.
Since the mounting section needs to reach deep inside, other action bases won't work with this structure.

Complete Hrududu II — size comparison with a cigarette pack

Underside

Even then, the Booster pod only exists in the blue Hazel II version,
so you can't put together a perfectly color-accurate Hrududu II with just a straight build.

Together with the HGUC Hrududu.
The styles are completely different, aren't they.

You can build the Woundwort Ra by applying two sets of Hrududu II.

Joint parts needed to build the Woundwort Ra

Additional Hrududu II parts that are needed.
These are also included in the HGUC Hazenthley Ra II, but if you want to build a complete Woundwort Ra,
you'll have no choice but to buy two HGUC Hrududu II Expansion Sets..

When building the Woundwort Ra, remove the claw section from inside the sub-arm.

Combine the various units and joint parts to assemble the configuration shown on the right.

You'll need one more white composite shield — you can either build another HGUC Woundwort and take it from there,
or borrow the one included with the HGUC Hazenthley II Ra.

Add joint parts to the outer thighs to allow the Hrududu II to be mounted there.

When using the composite shield in claw mode, you can spread the shoulders and lock it in place up top.

Next, let's apply it to the HGUC Hazenthley II to build the Hazenthley II Ra.

Joint parts needed to build the Hazenthley II Ra

Move the Hrududu II's mounting point all the way to the rear.

Attach a separate joint part to the back of the shoulder and relocate the beam cannon there,
then plug the Hrududu II onto the peg indicated by the arrow.

Borrow the Booster pod from the Hazel II and attach it to the crotch using a separate joint part.

Detach the beam cannon and composite shield from the existing Hazenthley II MA form.

Since two blue composite shields are needed, the instructions say to borrow one from the HGUC Hazel II —
but as you can see, the inner frame colors are different, so it looks a bit unbalanced.

Joint parts needed when applying the Hrududu II to the Hazenthley II's MA form

Attach the composite shields to both rear sides using joint parts as shown above.

then plug it into the hole where the beam cannon used to be and you're done

Underside