The Affinity Chart is a major game mechanic in Xenoblade Chronicles. It displays the party's affinity, or reputation, with a given area of the world as well as the affinity between NPCs. A higher affinity with an area allows more quests to be taken from that area, NPCs offer more items to trade, and discounts at shops. Achievements can be completed depending on the progress of the affinity chart as well. Finally, for each affinity star in one area more quests can be unlocked.
The Affinity Chart can be changed by completing quests. NPCs will change their description and their affinity towards each other, for better or for worse, and the party's affinity with an area will go up upon completing any quest, except for a few which will actually lower it. Note that the quests' unlocking is related to the number of people registered in the Affinity Chart: some quests still remain blocked until characters involved in it are spoken to and registered on the chart.
Many times, the player is given a choice between two quests. The affinity chart may change in accordance to which quest the player chose. This also take place in a quest with multiple choices.