He decides to move in with her.

"Ah!" Natsu said, pounding a fist down into an upturned palm as he came up with a simple, but great solution. One that would not only save money for himself and Lucy, but also...

"What is it Master?" Lucy asked.

"Happy and I move in here with you!" Natsu said.

"...eh?" Maid Lucy blushed, admittedly liking the idea, but unsure of the mechanics. "Um, Master, wouldn't that be more expensive for you, given that you own a cottage in the woods?"

"The cottage yes, just not the land it's on, I gotta pay a sort of rent for that myself, 48,000 Jewels," Natsu grumbled. "Money grubbing Magnolia officials," he muttered.

"Right, but this is a one bedroom place Master..." she replied.

"You're not trying to talk me out of this are you?" Natsu asked, raising an eyebrow.

"N-not at all Master!" Lucy denied. "I'm just bringing up the potential issues so you can make it work if you can and nothing comes back to bite you!"

Natsu thought it over, and smiled, glad he had someone as intelligent as Lucy, even if she was subservient to him, looking out for him."Right, well, that's easy enough, I can just sleep on the couch when your main persona is in charge, at least until I'm more intimate with you like that, or in your bed with you when I've got you triggered!" he answered.

"In that case, there are only two more issues," Lucy replied, thinking hopefully this might work in her current maid mindset. "My main persona agreeing to it, and not to mention my landlady stipulated this was a one person rental..."

"Your landlady I can handle, just give me her name, and a picture of her, and the rest I can do. As for your main persona... Well, I programmed you in the first place, it'll be easy enough to add a bit more programming to you to make your main personality accepting of having a roommate. Plus, this whole thing will give me more regular access to you," he grinned.

Lucy smiled, though took a moment to go over it in her mind in case there was another issue. Finding none, she kissed him. "You have great ideas Master..."