His idea, but slightly modified

To Natsu, Erza seemed a little stone-faced. She was clearly caring on some level, but she obviously had a sort of mask. A way she wanted the world to see her - as a powerful **** who was always in charge. Everyone else in the guild seemed scared of her on some level, whether that be in combat or overall.

But he wanted to see her with other masks, so to speak. So he opened up the Note.

"Any time Natsu Drangeel says 'transform' followed by either a person, type of person, or thing, Erza Scarlet will use her abilities to change into a suitable outfit for that person, then begin acting like them. He could say 'transform, maid' and she would believe herself to be a maid, and dress accordingly. He could also say 'transform, Lucy Heartfilia' and she would change into Lucy's clothing, and act like how she perceives Lucy. Or 'transform robot' would make her believe she's a robot. In any of these transformations, she will find herself submissive to Natsu. In her normal identity, she will be unaware of her transformations, but still want to listen to Natsu. She will return to her normal state if Natsu uses the transformation command followed by 'normal'" he wrote.

It was quite the essay - but he felt like it could be a ton of fun, and opened up a world of possibilities. It was definitely the most dynamic of his writings so far, but at this point he was beyond the mere experiments he had done before. And much like what seemed to be the rest of the guild, Erza was captivating... but in a different way. She was almost a forbidden fruit. Someone he knew he stood no chance against without the book.