A isolated facility suddenly explode and a airborne virus has been born and spread like wild fire without noticing at first there was not particularly any effects. After 1 month.. 2 months.. Something have happen to the new born infant babies all around the world..
Girl babies have grown 2nd gender, both can serve its function.
However the Boy babies there's no any changes from the outside, but after they have research the boy babies, its possible for them to conceived children but through the use of anus organ, it have developed functions from the inside.

After Several Years...
A fateful encounter happen between the new generation species, the "Other Half" bond...