2 Scenarios, each a different Mamono (to clarify: I'd be a one-woman person):
Scenario 1: Cupid
I'm sitting at my desk, looking at random things online until I stumble upon an article about NNN and learn about it. While reading through it, my Cupid wife enters the room.
"Oh; what are you looking at?" She then reads through the article, and I see her curious smile gradually droop more and more into a concerned frown. "Why are you looking at this?" She asks me the same way she might ask why I'm reading a history book or looking at some other random fact, but I can guess by her tone that she doesn't like what she's reading.
"Honestly, I just stumbled upon it. I don't know; it might be neat." I then turn to face her. "What do you think?"
She looks directly at me, but she doesn't say anything for a while. "...You know I'm not good at saying this stuff with words."
"Then... don't use words" I try to reassure her. She just says, "Okay". Next thing I know, one of her arrows is sticking out of my chest before it disappears. "Why'd you-" I say in shock before I find myself unable to think straight; my mind focused solely on my wife; her beautiful eyes, her long flowing pink hair... Overcome by something greater than myself, I get up off my chair and kiss my wife. In mere moments, she and I move to the bedroom and close the door. It is only the next day that I walk back to my computer and realize that I had left it on.
Scenario 2: Dhampir
Similar Situation; I learn about NNN by stumbling upon an article about it online, and my Dhampir wife walks in and sees it. As she reads through it, I wonder how she'll react: on the one hand, I don't think she'd like something like this. On the other hand, I know she likes a fun little challenge, and she might this as one.
"It sounds interesting," She tells me. "I suppose, in a weird way, it could even be a little romantic if we both take part." She then looks right at me, "Just promise me we'll more than 'make up for lost time' when it's over, right?"
Surprised that she's willing to do this, I just say, "Absolutely."
"Then I'm in," She says before kissing me. The first week is a massive struggle for both of us, but we manage through sheer determination; the same natural determination that got us through many fights against vampires and other cruel mamono we were hired to fight and force to re-evaluate their view of humans.
However, in week 2, we get hired by a town a few days away to deal with a Vampire that rules the town with an iron fist. Along the way there, our vehicle is forced off the road by a terrible storm. We're both fine, but we easily could've died. Eventually, we're able to get to the nearest town along the way and stop there for the night. After we enter the room we're staying in, my wife lies back on the bed and tries to relax. I look at her, and my mind can only think about how we both survived.
"Forget NNN" I blurt out, "Forget that dumb article." My wife just looks at me in surprise before smiling.
"I feel the same. Now, get over here." I lie down on the bed, and we proceed to make up for the time we lost during the previous week.