Almighty Tallest Miyuki's Reign

Tallest Miyuki
Tallest Miyuki was to be introduced in the episode 'Trial' via flashback where it was to be revealed that she was one of two Tallest prior to Red and Purple. The script was read aloud at InvaderCON and shows that she was one of two heads of state to be killed by Zim's Infinite Energy Absorbing Blob, the other being her successor Spork.

What We Know
Miyuki commissioned the construction of 'The Massive'. It was being built by Vortian Engineers before they where Conquered by Invader Larb under the orders of Red and Purple. She was present at Vort Research Station 9 where Zim was working, and his monster blob killed her. His role in creating the beast would not be discovered until his 'Existence Evaluation'. She was succeeded by Spork, who was also destroyed by the same type of beast (again made by Zim). She is the only female Tallest mentioned so far, and the earliest Tallest we know of. Her character is named after storyboard artist Miyuki Hoshikawa.

She was a Scientist
Some speculate that before she was 'Almighty Tallest' she her self was a scientist; thus her cooperation with the Vortians.

Planet Jackers
Some speculate that Miyuki was the Almighty Tallest during the time when the treaty with the Planet Jackers was made. The terms of the treaty forbid the Planet Jackers from destroying worlds marked for conquest by the Irken Empire, which has the side effect of sparing those worlds and their inhabitants a fiery demise in the sun of the Planet Jacker's home system.

Peaceful Rule
The fact that Irkens, a war like people, cooperated with at least one other species during her time as Almighty Tallest seems to imply that it was a time of peace for the Irken Empire. The fact that the Head Scientist of the Vortian Research Station presented an 'Infinite Energy Producing Thingy' seems to support the idea though designs for the BLUDGEON CLASS fleet leader (commissioned by Miyuki) where also presented to her. Lard Nar, a Vortian and future leader of the Resisty after Vort's conquest by Red and Purple, was the main designer of the ship that became 'The Massive'.

GIR
Due to Miyuki typically being depicted in a light blue and silver it's speculated that GIR's line of Irken Robots where constructed during Miyuki's Reign and latter scrapped for the newer models produced under Red and Purple's Reign.

Observers
It's speculated that Miyuki was interested in observing other species for scientific purposes, and that some of her ideas where incorporated into 'Operation Impending Doom 2'- namely the infiltration aspect of the plan.

Contact with Professor Membrane
Some headcanon involves Miyuki having contact with Professor Membrane, and this contact playing a role in his advanced technology on Earth. Miyuki has been shown to cooperate with none Irken scientist. This headcanon is used to explain how Dib was able to overhear the opening ceremonies of 'Operation Impending Doom 2'- the speculation being that he, as he sometimes does, borrowed one of his dad's computers and that Membrane never bothered to change the channel. The idea is that Membrane has the computer Dib used, and such is why Dib hasn't been able to record other events from Irk- as he no longer has access to the channel and with Zim present has abandoned pursuit of trying to find it manually. Why waste time with that when an Alien is next door? It also explains why Dib's computer operating system is the same as the one used by the Irkens- it is of Irken origin.