Everyone's emotions influence the setting directly, since their emotions manifest as different effects - changing temperature, conjuring flowers, causing the earth to crack, etc.
It can also change how the game goes, since there's giant emotion gods that are influenced based on if the populace is feeling more positive emotions or negative emotions, which can potentially mean Boss Fights
(Actually, IIRC - it was either you or the mod who said that Relm would be the best fit there? But if your heart's set on Terra, that might be okay too. Can always ask/app and see what happens. :3)