DEAR SPACE (RJ01372522)

However, aboard that ship awaited humans, creatures, and machines exposed to and contaminated by an unknown substance known as “EX Cells.”
These monsters, driven by self-replication and violent instincts, lurked in the shadows…

The protagonist’s lover, Clau, was the first to be infected by the EX Cells and had become the “Mother.”
This Mother commanded a group of uniquely transformed women—those who had undergone special mutations—known as “monster girls.”

In the protagonist’s hands was the only weapon capable of suppressing and neutralizing the EX Cells:
the experimental wave cannon, Prototype Wave Cannon Type-R.