If you chose and play as the Hero:
After a bunch of cut scenes, meeting and chatting with Isabella on the east wing of the first floor of the Hall, and then retired back to your room (the doors are locked at that point so there was no way the Hero and the Heroine can go to Marsh Cave). Another short cut scene of the Hero's nightmare/past, the Hero wake up and as he turn to check on the Heroine... he realized she wasn't on the other bed and wonder where had she gone off to. (or in the Hero's point of view, she was either taken or kidnapped by the Count of Vinquette Hall). Leaving the room; again, another short cut scenes show one of the butlers exiting the west door and unlocking the east door downstairs.
Afterward (the player can chose to check Isabella's room again or go forward to find/save the Heroine), if you chose to go to Isabella's room again, the Hero won't find her, but instead her diary which tell you a little bit of her past.
If you chose and play as the Heroine:
After similar events and cut scenes as the Hero's side of the storyline but only different when the Heroine asked Isabella if she is dating the Count of Vinquette Hall which Isabella answered either sarcastically or without a doubt. After chatting with Isabella and retired back to their room; the Heroine pointlessly argue with the Hero to stay awake after he commented that " I haven't slept on a bed for a long time" and fell asleep on the bed on the right (west) side of the room. Hopeless on waking him up; the Heroine decide to take a short nap. But then her dream of the past came up to her again (another cut scene), so the Heroine quickly woke herself up as she can't sleep without dreaming of that again. Then the Heroine heard the Hero talk in his dream of his past which was the same saying of the young boy that the Heroine had attempted to flee with years ago and suddenly realized that the Hero is the young boy that she thought had died with his parents. The Heroine then blame herself for his parents' deaths and apologize to the Hero (still sleeping and dreaming) then suddenly something made a noise from outside their room.......another cut scene (again).
Afterward (the player can chose to check Isabella's room again or go forward to investigate and find out what that butler was talking about), if you choose to go to Isabella's room again, the Heroine won't find her (making the Heroine concerned about Isabella's safety), but instead her diary which contains a little info of her past.
She later encounters the Dark Lord and, apparently smitten by him, joins him. This results in a later encounter between her and the team of Heroes, where she threatens to attack them to prevent them entering the castle. After the situation is defused she is next seen during Dark Lord's death. After Goremand consumes Dark Lord's soul she changes into a cat like beast and attacks Goremand. The battle is left inconclusive, but she is seen alive later when she grants her strength to the heroes alongside many others they have encountered during their travels.
As written from Isabella's diary.
That cad. I thought I'd get to see him, and then he runs off to the human world. What nerve!
what ARE they thinking?
In other news, I heard that three Gemma Knights brought down the Vandole Empire and ushered in peace.
Among the three Gemmas was a minstrel named Granz with a magical voice, which reminds me...
That primate princess was going to look into that human, Granz...
Did something happen to her in the human world?
Either way, this must be investigated...
From either reaction from the Hero and the Heroine, we can assumed that Isabella is around the same age as Lord Granz, Lady Medusa (?), Count Lee and anyone else around 20 years ago.
After the Hero/the Heroine finds the Moon Mirror, kill the hydra (or what its call for the two headed dragon) at Marsh Cave, and saving the water spirit, Undine. Bring the Moon Mirror to Isabella at Vinquette Hall (when the gate open again at night) and Isabella will explain to the Hero/the Heroine that it's used to see people's true colors and then asked the Hero/the Heroine if she can keep it, but suddenly Isabella changed her mind and told the Hero/the Heroine to keep the Moon Mirror (which later broke).
A very similar looking character that also goes by the name Isabella (at least when posing as a human) appears in Seiken Densetsu 3. They also share the ability to change into a cat like beast. It is unclear if the two characters are supposed to be one and the same person, or if it is more of a cameo.