The region is based off the Chubu Region of Japan.
(Obviously edited, seeing as the Chubu Region has water on two sides and
the Mantji Region is surrounded by water on three.) In my mindset, I
like to think of the region being south of the Johto/Kanto landmass and
north of Hoenn. (This works because Hoenn is an island.) Coincidentally,
the Chubu Region in Japan is between the real life Kansai Region and
Kanto Region. (Johto is based off of Kansai and Kanto is based off of
Kanto, duh.) This would obviously create a problem because Kanto and
Johto are connected in the Pokémon World, thus I moved Mantji southwest
of Johto. This is why the Mantji Region bears so many physical and
pokémon-related aspects of the Johto region. There is also a backstory
as to how the Mantji Region was found; a pokémon trainer (actually a
pokémon master) stumbled across it whilst traveling through Johto. The
location also explains the fact why multiple Johto pokémon are found in
this region, as well as some Kanto and Hoenn. No Sinnoh pokémon however,
because that would be incongruous with the location.
We will make a game page soon!