http://vndb.org/v1111
Description:
Long, long ago...
In a place where castles were constantly being invaded because of war,
there was a king who thought about the damage castles suffered.
He thought of something no one else had and realized his difficult idea.
Use castles to fight castles!
He would move his castle straight to his enemy's and attack.
Already having quite a bit of national power, he took control of the continent in the blink of an eye.
A few hundred years have passed, and that king is no more.
What remains is moving fortresses and the warring countries that use them...
A tiny, tiny kingdom, consisting of one moving fortress, Mamatoto.
The king, [Kakaro], was once strong enough to hold the title of Warrior King.
The one who managed the entire country, and was known as a
skilled general by other countries, was the king's son [Nanus].
After many battles brought their national power down to its very limit, now they're surviving by using
their incredible speed and General Nanus' power to run from other countries' large moving fortresses.
The [Forland Continent] where such large battles continued endlessly.
In the Northeast, there was a region called the [Monster Realm] inhabited by dreadful things.
There existed a huge, mysterious cave.
Inside the [Cross-Cave] is, just as the name suggests, a cross-dimension.
It's said that stepping into the cave is fatal, and that no one ever returns alive.
There's no lack of people who gather armies and push into the cave to see what its reaches hold,
but the giant cave has continued to swallow such people whole.
Kakaro, the king of Mamatoto, is another who thought to challenge the [Cross-Cave].
This story begins after his son Nanus invented something
that could grant his father's wishes...