Why was Nikolai chosen to be the one who kills everyone at the end?

I get Richthofen was afraid of sacrifice, he couldn't bring himself to do it. But why did he pick Nikolai to be the one to poison everyone? Wouldn't the more honorable Takeo be a better choice, a person raised in a society that has a history of sacrifice for the greater good? Or even Tank is a better choice than Nikolai. I understand it's a different universe but we've seen Nikolai break in Gorod Krovi as a result in the deaths of those close to him. It just feels like the worst pick of the bunch.

Then again it's not the worst thing about that ending