Impregnable Dreadnought

Impregnable Dreadnought summary:

Year 1999.
Due to a meteorite collision, Holes connecting Earth to a parallel world opened.
Lemuria Confederation, one of the two major powers in the parallel world, launched an invasion against Earth, disregarding their bafflement.
The Earth’s side fought hard against the parallel world’s magic, enlisting aid from Astoria Kingdom which was the other major power from the parallel world, and succeeded in developing magic technology.
With the appearance of magic technology, the war fell into a stalemate. At last, an armistice between Lemuria Confederation and Earth was established in year 2002.
And then 50 years later.
Lemuria Confederation and Earth repeated waging wars and declaring truce while somehow maintaining balance.
In the middle of that, at the border zone of the parallel world’s Astoria and Lemuria, one j.a.panese boy descended.
His name is Yuuki Mamoru.
Nicknamed Sir Dreadnought.
One of the 48 knights who supported Astoria Kingdom.