In order to keep things simpler to write and code, all character storylines are determined by their own stats (Int, Fit, Charm, Guts, Bimbo). These stats can be affected by the player and the player's stats as well, for example studying with Twilight helps both raise Int the higher their own Ints are. So instead of stress maybe Twilight's story is tied to her Fit and Int, with a good ending resulting in her having enough Int to pass whatever exam but also enough fitness to not have her stomach eating itself out of undernourishment and exhaustion.
something like that