Parallel Universe

The two Universe exist in the same time, same place but different ways and different year. The year 4020, the year works backward while the year 2020 works forward. They are 2000 years apart but every after 10 years the two different universe collided and it happens in the normal cycle of 1 year and the people in 2020 will switch to 4020 and vice versa without them noticing it.

To maintain the balance of two Universe the people from 4020 and 2020 should make it to the portal before the switch of both worlds or else if the two person exist in the same world, same timeline; one should sacrifice to keep the balance of both worlds.