Lore

This is just a theory.

In Sipho which is somewhere flooded with water, you play as a parasitic organism from unknown habitat that has taken control of an innocent Sipho, possessing it and becoming an organism with great mutation ability, being able to kill the newly created ecosystem of the flooded area.As you can see right here, there's an effect called possessed.

The part about the flood came from the leaves on the trees in the plant area. They were undecayed meaning that the area was recently flooded. There are also hints of human inhabitants in the area.