So a kaiju (怪獣) is any kind of big, terrifying, and seemingly undefeatable monster in fiction. The kind we're most familiar with, like Godzilla, are daikaiju (大怪獣) which specifically refers to the giant kind. They vary from being fairly intelligent to being animals, and tend to attack cities and things, leaving devastation behind.
This is a pretty loose definition, though. So...
In pretty much any version of the story, the Tripods from War of the Worlds are basically unstoppable eldrich horrors which wreck everything in their path until they all get sick and die.
They're mechanical, but so is Mechagodzilla. They're from space, but so is King Ghidora.
@InvaderXan hrm… the ones from Neon Genesis Evangelion skirt the line, because of how much of their own willpower they have
but from what i gather, most mechas affect the pilot in a way, the longer they pilot it
it seems to be a core element of what defines the genre, or at least what makes a truly powerful mecha
@InvaderXan so i know nothing of the Golem myth
but it keeps popping into my mind, so here goes nothing
the Golem is made from clay
but once you breathe life into it, it, well acquires life, but it can also acquire a will separate from the one who awoke it
similarly, the life you insert into a mecha is the pilot, then it comes to life
but often the will of the mecha is not entirely the will of the pilot
The Xandalorian
eena meena me