Levy happily accepted the insoles. She knew her feet didn't smell bad, but that was only because she used her word magic to inscribe, "clean" onto her feet. As soon as she left the guild that day, she removed the "clean" insignia. She instead decided that she wanted to use the Insoles for what they were meant for, and she inscribed, "smelly" into her feet. Natsu noticed the scent right away. It kept increasing more and more. Levy kept writing, "smelly, smelly," , "stinky, stinky", "sweaty , sweaty", "dirty, dirty", and she ended up having some of the most disgusting feet in Magnolia. Natsu was having a really rough time handling this. He was already smelling so many smelly feet at once, he had forgotten what anything besides feet smelled like, what anything besides feet tasted like, and what anything besides feet looked like. He even began to hear whispers in his head saying, "feet, feet, feet." It was driving him insane.
Levy kept this up and was increasing surprised at how much the insole could handle. Eventually, when it was time to return the insoles, she wrote, "Save Changes". All the foot smell and foot sweat she had built up was drained into Natsu permanently and "Saved" into him. Another scent to his collection. There was now only one girl left to try out the insoles. Erza secretly took Natsu aside and said, "Listen here Natsu, you are going to experience smelly feet that rival mine, some even say they are worst. She is known as, 'The demon, Mira-Jane'. If Natsu could scream, he would. Erza knew however, that MiraJane would not allow any living this to be tortured under her feet, for she knew how potent they were. And so for the time being, Erza thrust Natsu into her own boots. Natsu thought, "Not again! I can't handle Erza's feet! It's too much! Too much! Someone! Anyone! Please! HELP ME!". Erza only smiled and placed her sweaty bare feet into her stinky boots. In the mean time, she plotted, waiting for Mira-Jane to lower her guard.
One week later, she attacked Mira-Jane, and they entered into an all out brawl. Erza however, went through with her plan, and during the fight, she pulled of Mira-Jane's boots. The guild cleared out immediately. There were even people outside warning others from entering. It was the thickest, most disgusting smell anyone could fathom. The scent of feet was overwhelming. Just then, Erza pulled off her own boots, and the two people with the stinkiest feet in all of Magnolia were now bare footed. Some poor soul walked ran into the guild at this time looking for a job. Unfortunately, he ran right into the scuffle and got kicked simultaneously in the face by both Erza and Mira-Jane, who said in Unision, "Don't Interfere!" For the good second that the guy had 4 bare soles in his face, he thought his life was over. Never had he experienced something that disgusting. The sweatiness, the scent, it overloaded his sense. He was knocked out for a month, unfortunately for him, he was having a constant nightmare that Erza and Mira-Jane were rubbing their feet in his face all the time.
Mira-Jane quickly became embarrassed about the scent in the guild, and reached for her boots. Erza got in a quick distracting strike, and swapped Natsu into her boots. They finished up the fight, and Mira-Jane noticed how much more comfortable her boots were, unaware Natsu was in them. Natsu was in pure hell. It was terror. He was crying inside his mind. It finally broke him. He couldn't handle it, he just wanted to die. Natsu noticed that in addition to all the girls who branded him before with their foot stench, he know smelled Erza's as well ALL the time. He wondered when she could have done that. It turns out that in the week Natsu spent inside Erza's boot just then, she had been requipping him into all of her footwear, and pushing the magical power of her feet into him, effectively branding him with her feet. Yet another sweaty feet that he must smell permanently.