See? With sentiments like that being presented, he can't possibly find it in himself to doubt how sincere Kai's affections are.

If the flush that's hit his cheeks isn't from kiss number three, it's definitely from the overwhelming joy and warmth those words stoke within him. That he's worth returning to. That he can be trusted with being a safe haven. It's intense - enough so to twist his stomach up, but that gut reaction of it potentially being too huge of a responsibility to trust him with is drowned out with how thoroughly he wants to hold on to that trust as tightly as possible. Doesn't Kai deserve a home he wants to come back to, after all? They've agreed before, it's not the place so much as the people there, and if Shinji can be that... he desperately wants to give it to him.

And so, he nods slightly, mouth drawn tightly with a barely constrained smile as he tries to figure out what he could possibly say to that.

"And I'll welcome you back every time," is what he decides on, a sheepish but sincere mumble. "No matter what."