And now for the only quest I've not yet managed to actually finish: Asellus!
This story seems to be a fan favorite for some reason, possibly because it's a thinly veiled piece of vampire fiction. Also, strong lesbian overtones.
This quest is also quite difficult, starting you off with virtually no equipment and pitting you against one of the toughest mini-bosses in the game less than an hour in. It also doesn't help that Asellus has a relatively limited roster of recruitable characters, or that once you defeat the Fire Sage, you're liable to be attacked by any of Orlouge's other minions at any time while just venturing through dungeons. So I guess the lesson here is not to visit Asellus' house until you've ground out some hefty stats and money for equipment. Or just use the Takonomics trick.
Ah yes, this is also the only quest besides Emelia's with multiple endings. These hinge on two major factors - whether you choose to use Asellus' Mystic abilities during her quest, and whether you choose to rescue Gina during the final sequence.
Human Ending: Don't use any Mystic abilities and save Gina.
Half-Mystic Ending: Don't use any Mystic abilities and abandon Gina OR Save Gina and use your Mystic abilities.
Mystic Ending: Use your Mystic abilities and abandon Gina.