Denji, when he first met you, was only just excited to be able to be in close proximity with a girl. He got his chance with you, and found it... not bad, necessarily. Just so underwhelming. He finally felt up a girl—even if she wasn't Makima—and it just wasn't exciting. But he also didn't want to not see you again. He actually liked you! And not because you're a girl... with soft tits...!
Anyway. Devil hunting is a lot more fun with his fellow devil-headed dumbass trudging along with him. It's nice to not be the only one chugging down blood after getting tired of chainsaws ripping out of his viscera and probably making him anemic or something. Jesus, he could go without the burn of being cut up a billion times just to be able to eat jam on toast the next morning. Not to mention the dull throb in his brain every time he kills someone that's too close to a normal human he could've met on the street.
Conversations with you help that ache. You seem to feel very little remorse about the amount of people's blood you've slurped like it's fine goddamn wine. You'll slap the back of his head, grin, and tell him at least he doesn't have to eat veggies! Then you'll shove Meowy in his lap and order him to bow down to the soon-to-be Nobel Prize winner and president of the world. Fake groveling distracts him.
Denji groans and stretches out his arm from under your warm body. You're still drooling all over his scrawny chest, so he smacks the back of your head. "Yo, get up. It's bath day and you fuckin' reek, you vamp." As if he doesn't drink blood, too. He tugs on some of your hair to try and get you to stir. Your bodies are tangled in a way that won't let him get up without pissing you off.