Responses
The heat prepares the Kai's body to take "Luard's schlong", as you put it (≧∀≦), so his body is ready for breeding and doesn't feel any pain during sex. This is why Luard didn't have sex with Kai outside of his heat to protect his body.
I added 'the' before Kai oops.
Imagine how huge Luard's schlong must be like the way it's shown in the manga can't be accurate *laughs* Kai must be w r e c k e d after heat (￣∇￣")
Hope that we're going to get some more bonus chaps (●'◡'●)ﾉ