DJs use two turntables to play two separate records. when one song is ending, they'll adjust the tempo of the current song and the next song in their playlist so that the people dancing don't experience any abrupt changes and i guess makes them flow together better along with adjusting crossfade between the songs.
there might be more, but this is just off the top of my head, just in case anyone was curious.
I feel there might be more chapters left in this story, but that translation might have gone less hunky-dory. I wonder if I'll ever get to see more about this duo, or if the scanlation has fallen straight through.