Offering, Sacrifice
If you take a cow's life you're turning it into an offering. In the old days, cows' lives were given to the gods as offerings pretty often.
Picture yourself offering the cow's life up to the god(s). It's a good thing we don't actually have to do this anymore, you think.
せい
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You prepare the offering with your holy blue saber (せい). Normally this would be gruesome, but your saber glows and the cow's life shoots up into the sky without you laying a hand on it.
Thanks to the mercy of your saber, the offering is quick and painless. A normal saber, however, would have cut that cow to bits. Like, really just wrecked it. Good thing we didn't make you think about that, huh?