Here's hoping Yuuka doesn't get pissed at Mokou and take up trying to kill her as a personal challenge. *shudder*

I'm more worried about Yuka. If she gets upset and tries to kill Mokou for some reason, and get more angry each time because Mokou can't die so she resurrects, Yuka might overheat and catch fire from trying so hard.
Then there will be no more flowers in Gensyoko.

And the ecology of Gensokyo slides slowly into ruin. Great.

Stay on her good side, Mokou.

Hey, they're getting along pretty well.

Maybe the reason is Mokou (and Kaguya, but she rarely leaves Eientei) is the only one human that wouldn't be afraid of her.

I don't know, I'm sure Yuka would eventually pound Mokou to the point where she'd be in too much pain to move for a few years.

As long as Mokou doesn't use her power around Yuka's field she'll be okay.