Mulberry 8

Mulberry 8 as seen from space (darker planet on the left, hidden behind Mulberry 7).

Mulberry 8 is a binary planet to Mulberry 7. On this planet, mecha-people are the rulers and humans are their slaves – this has been the situation for a long time, as Hoshiro admits he doesn’t know any other life. Mulberry 8 is ruled by feudal lords, two of them were introduced: Mecha-Count of Gear Nation on the East and King Chamechamecha on the West. It is not clear whether they are the only two rulers or if there are more.
The robots engage in fights on Se-Mecha-Hara battlefield – the bodies they destroy during these are discarded and new ones are paid for by exporting the planet's clams collected by humans. This, according to the Mecha-Count, allows them to progress. During these battles, missiles and beams are forbidden – only traditional weapons can be used as per Tao of Mecha.

Se-Mecha-Hara field.

After a revolution lead by the humans of this planet, people and mecha agreed to live in harmony and decided to improve their tourism, focusing on their local clams. Clam-shaped bathroom utilities are now available for humans to use.

Robots and humans of Mulberry 8.

This planet was visited in episode 8 and the developments after the revolution were mentioned in drama CDs 4 and 6.

Trivia

Mulberry 8 is named after Kuwana, which was also a station of the original Tōkaidō – kuwa means mulberry. Nowadays Kuwana is known for clams, but also traditionally for metal casting industry.

Mulberry 8 also owns modern military weapons, seen stored in the King’s castle – and these are kept in good shape, proved when humans hijack them. The King says these are not to be used in their internal battles, but for defending their planet. This, especially considering the good state of weaponry, could suggest Mulberry 8 is either having issues with external invasions or suspects there is a risk of it – but it is not said who might be their enemy and the topic is not discussed in more depth than the King's brief comment.