Why dont they just inject Kiri's blood in her

because that would be the smart thing to do plus it would end the story to quickly and what's the fun in that

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It's true that we don't know what we've got until we lose it, but it's also true that we don't know what we've been missing until it arrives.

When I die, I want to go peacefully like my Grandfather did, in his sleep -- not screaming, like the passengers in his car.

I'm thinking of injecting "something else", you know...

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Furthermore, what if they have unsuitable blood type? They cannot do the blood transfer.

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And who's to say it's in Kiri's blood?

Too risky. He needs to make a dry run with Sister Heine first to verify it's effectiveness. Sweet sweet verification...