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Since you mention nanomachines, check out utility fog. It would give you the ability to make things appear and form magically. The Yggdrasil tree is a giant nano factory created by the bomb, which both builds and powers the nanomachines.
The factory could also build other nanomachines. Some that take stuff apart, some that build, some that fight by entering the targets body. It would use the utility fog to transport them where they need to go. The ones that build and take stuff apart are what is doing the teraforming.

Edit to summarize the comments:
Demons are caused by things left over from the war:
Biological germ weapons that have mutated and now cause mutations, madness, copying genetic traits from one creature to another.
Biological monsters created in a lab and released onto the battlefield.
Autonomous machines created to hunt enemy soldiers, now roaming and killing indiscriminately.
Super solder programs gone wrong, biological implants with horrific destructive capability.
Parasitic machines that burrow into living creatures, take them over to create a cyborg. Once the host dies the machines cut their way out so they can hunt for a new body. (actually, this one works for being "demon possessed", with a degausser as exorcism equipment)

Since you mention nanomachines, check out utility fog. It would give you the ability to make things appear and form magically. The Yggdrasil tree is a giant nano factory created by the bomb, which both builds and powers the nanomachines.
The factory could also build other nanomachines. Some that take stuff apart, some that build, some that fight by entering the targets body. It would use the utility fog to transport them where they need to go. The ones that build and take stuff apart are what is doing the teraforming.

Edit to summarize the comments:
Demons are caused by things left over from the war:
Biological germ weapons that have mutated and now cause mutations, madness, copying genetic traits from one creature to another.
Biological monsters created in a lab and released onto the battlefield.
Autonomous machines created to hunt enemy soldiers, now roaming and killing indiscriminately.
Super solder programs gone wrong, biological implants with horrific destructive capability.
Parasitic machines that burrow into living creatures, take them over to create a cyborg. Once the host dies the machines cut their way out so they can hunt for a new body. (actually, this one works for being "demon possessed", with a degausser as exorcism equipment)

Since you mention nanomachines, check out utility fog. It would give you the ability to make things appear and form magically. The Yggdrasil tree is a giant nano factory created by the bomb, which both builds and powers the nanomachines.
The factory could also build other nanomachines. Some that take stuff apart, some that build, some that fight by entering the targets body. It would use the utility fog to transport them where they need to go. The ones that build and take stuff apart are what is doing the teraforming.

Edit to summarize the comments:
Demons are caused by things left over from the war:
Biological germ weapons that have mutated and now cause mutations, madness, copying genetic traits from one creature to another.
Biological monsters created in a lab and released onto the battlefield.
Autonomous machines created to hunt enemy soldiers, now roaming and killing indiscriminately.
Super solder programs gone wrong, biological implants with horrific destructive capability.
Parasitic machines that burrow into living creatures, take them over to create a cyborg. Once the host dies the machines cut their way out so they can hunt for a new body.

Since you mention nanomachines, check out utility fog. It would give you the ability to make things appear and form magically. The Yggdrasil tree is a giant nano factory created by the bomb, which both builds and powers the nanomachines.
The factory could also build other nanomachines. Some that take stuff apart, some that build, some that fight by entering the targets body. It would use the utility fog to transport them where they need to go. The ones that build and take stuff apart are what is doing the teraforming.

Edit to summarize the comments:
Demons are caused by things left over from the war:
Biological germ weapons that have mutated and now cause mutations, madness, copying genetic traits from one creature to another.
Biological monsters created in a lab and released onto the battlefield.
Autonomous machines created to hunt enemy soldiers, now roaming and killing indiscriminately.
Super solder programs gone wrong, biological implants with horrific destructive capability.
Parasitic machines that burrow into living creatures, take them over to create a cyborg. Once the host dies the machines cut their way out so they can hunt for a new body. (actually, this one works for being "demon possessed", with a degausser as exorcism equipment)

Since you mention nanomachines, check out utility fog. It would give you the ability to make things appear and form magically. The Yggdrasil tree is a giant nano factory created by the bomb, which both builds and powers the nanomachines.
The factory could also build other nanomachines. Some that take stuff apart, some that build, some that fight by entering the targets body. It would use the utility fog to transport them where they need to go. The ones that build and take stuff apart are what is doing the teraforming.

Since you mention nanomachines, check out utility fog. It would give you the ability to make things appear and form magically. The Yggdrasil tree is a giant nano factory created by the bomb, which both builds and powers the nanomachines.
The factory could also build other nanomachines. Some that take stuff apart, some that build, some that fight by entering the targets body. It would use the utility fog to transport them where they need to go. The ones that build and take stuff apart are what is doing the teraforming.

Edit to summarize the comments:
Demons are caused by things left over from the war:
Biological germ weapons that have mutated and now cause mutations, madness, copying genetic traits from one creature to another.
Biological monsters created in a lab and released onto the battlefield.
Autonomous machines created to hunt enemy soldiers, now roaming and killing indiscriminately.
Super solder programs gone wrong, biological implants with horrific destructive capability.
Parasitic machines that burrow into living creatures, take them over to create a cyborg. Once the host dies the machines cut their way out so they can hunt for a new body.