Persona 3 FES Request 84
For this Request what you will need to do is first head to your Dorm and to the vending machine inside. Other vending machines work as well but this is the primary one I know of with the soda we're after. Once you're at this vending machine you'll want to purchase a total of 20 Cielo Mists.
It'll be a time consuming endeavor but just stand there and spam X for a minute or two until you have enough of them. If you can't find the vending machine or otherwise need visual support take a gander at my picture below.
After you've purchased enough Cielo Mist you'll want to head over to Port Island Station and to the left of the vending machine. Right next to the vending machine (as seen in the picture below) you'll find a girl on the ground that is clearly suffering from Apathy Syndrome. Speaking with her will start a chain of dialogue that eventually leads to you giving her all 20 cans of Cielo Mist.
Your request will be completed at this time and you'll be able to return to Elizabeth for your reward. Which just so happens to be a Maid outfit for Aigis.