Yikes! For those who aren't familiar with the Einherjar, as I wasn't, here is the wikipedia entry for Einherjar.
Warriors from those who die in battle? If I had to guess, I'd expect it to be a combat cyborg process. You could go with volunteers, or, you look for soldiers who have suffered grave injuries and make them an offer. "Your friends and family will have to think you died. But in return you get a body that is faster and stronger than when you were young. You will then join a unit of others who have accepted the same offer where you will become the toughest special forces unit in the entire Ground Forces."
Or, perhaps. "We need some volunteers. You, you, and you. You three just volunteered. Get in the tubes."
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Will the transhumanist future have catgirls? Does Japan still exist? Well, there is your answer.
Warriors from those who die in battle? If I had to guess, I'd expect it to be a combat cyborg process. You could go with volunteers, or, you look for soldiers who have suffered grave injuries and make them an offer. "Your friends and family will have to think you died. But in return you get a body that is faster and stronger than when you were young. You will then join a unit of others who have accepted the same offer where you will become the toughest special forces unit in the entire Ground Forces."
Or, perhaps. "We need some volunteers. You, you, and you. You three just volunteered. Get in the tubes."
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Will the transhumanist future have catgirls? Does Japan still exist? Well, there is your answer.