Why the hell (no pun intended) not?

Kazuma paused, considering Vanir's extended hand for a moment. He was still wary, he heard enough tales of people making deals with demons and devils back in his own world to be a tad skeptical... But then again, Vanir had already specified that he wasn't asking for Kazuma's soul. This was merely a business deal. What was the worst that could happen? Vanir short changing him? He looked at Wiz, who was bubbling with excitement. She'd been nothing but friendly with him despite his... partnership with a goddess who kept trying to destroy her. And she seemed to trust Vanir well enough... Ah, what the hell?

"Screw it, you have yourself a deal, so long as you don't try to screw me over," Kazuma grinned, shaking Vanir's hand.

"Wonderful!" Vanir beamed.

...

A few days later, Kazuma was at home with the first of the products he had made for Vanir, who had provided the materials once he had laid out what the product was: a kotatsu table. A simple Japanese thing, it was a table frame with a heavy blanket attached, and a table top on top, naturally. As was stated, it was a simple enough creation, but hoh boy, was it a popular one in this time of year. It was still a cold winter, so Vanir and Wiz had actually had some trouble keeping them stocked once Kazuma had given him the prototype. Wiz was jubilant about her shop finally starting to get out of the red, though she had endured a tongue lashing from Vanir about her lack of business sense that had gotten her there in the first place.

And of course, Kazuma got a nice chunk of change himself, as well as having made a personal kotatsu... Only problem was that it had gotten him lazy... Well, he was already lazy, but now it was more enabled. Having all the money he needed for the foreseeable future, he spent most of his time at the kotatsu, just trying to stay warm, and only sexual matters with his harem could currently motivate him to move from the spot.

Speaking of sexual matters, there was Yunyun... She had moved in well enough, and despite a few arguments with Megumin, was getting along with the group just fine... Plus there were the challenges she gave Kazuma, and the reward for him pulling a fast one on her, three additional times from the first so far...