The landmass is not Makai. The landmass is Mataraiku('phucked the spellin' up, totally). Makai is officially the dimension Matarikou is in. We don't know how big Makai is but Makai is the term in general for Mataraiku and the other dimensions in Makai wit gate ways located on Mataraku. Other dimensions like the space in between some waterfall. The space in some volcano and some other world wit demon like creatures that the oldest Makai noble used to communicate wit.
Despite Belial bein' one wit Makai, he has his own seperate body. There's this badass official pic of'im fightin' Demetri in his true form. Even Demetri's true form looks like a newborn baby to Belial and in the pic you can see that Belial seals off his top arms by simply crossin'em. There are finally more pics but they aint as detailed.