Tales of Xillia

You need to finish 800 battles with a food effect active. To gain an effect from a food, simply select it from the Items menu. Different foods provide different effects and last for different numbers of battles. You gain access to food fairly early in the game. The trick to getting up to 800 food effects is to stock up on food at every food vendor you come across, stay stocked up, and eat food whenever the effects of the previous food are gone. You can see how many more battles a food effect will last on the stats menu in the bottom right corner, in yellow, next to the time. If you try to use a food before the effects of the current food are gone, the game will warn you that the new food will cancel out the effects of the current food. Only do this if you really want a different effect for the next battle. (For example, if you're about to fight a boss and want the double experience from a Spicy Chicken Roll instead of whatever active effect you have.)

Also keep in mind that each food comes in three sizes (Small, Medium, and Large) and you can only hold one of each food in each size. There will be very few foods available from the start, but as you expand the food vendor, more and more will become available, and they'll start to drop in price. The only difference between the sizes is the number of battles the effect will last.

If you make sure to have a food effect active constantly and you're playing the game long enough to achieve everything needed for all the other trophies, this should unlock near the end of your first playthrough, or at least be close enough to unlock it in the post-game stuff. You can check your progress in the Records or Titles option of the Library menu.