Sylphiel is your average sweet, gentle, and kind girl. Growing up with her father has made her into a proper and modestly polite woman, though she may have become sheltered by her father's unconditional love and from being secluded within the walls of Sairaag. She's very helpful and friendly to those around her and always wants to give a helping hand to people who are in need because she does not like seeing anyone to become needlessly hurt.
With her kind heart and from paying attention to people, she can be quite intuitive to someone's thought or feelings as if they were her own and sometimes knows what they feel before they do themselves. She knew before Lina herself knew, that Lina was in love with Gourry. This makes her the most feeling of the Slayers characters and her faith in her loved ones is unyielding. She believed Gourry was not the criminal Eris' rumors made him out to be and she knew her father would not harm her even though he was Phibrizzo's slave.
In some ways, Sylphiel is still a child at heart; the way she squeals in excitement over the chibi Gourry and the stuffed teddy bear she found proves this. Sylphiel is also quite the romantic since she wishes to one day become a bride and have a lovely wedding -- with Gourry as her groom of course. Also, Sylphiel can get into things that are a bit over her head, such as when she intervened Zangulus and Gourry's fight by throwing herself in the way when Zangulus sent a blow at Gourry. She has always placed the well being of others above her own.
She has a vast knowledge in the magic arts though her actual skills could use work. As a female who was raised in a peaceful city, she is not extremely skilled in battle and can be easily overpowered. Her main area of expertise is in white magic especially with healing spells such as Recovery. She couldn't cast a proper Flare Arrow at first but she does improve later because of her determination to be strong like Lina and has eventually mastered the Dragon Slave after vigorous training.
Her biggest flaw is that she always wears her heart on her sleeve and enemies can use that against her since she is quite vulnerable to her emotions. Because of her kind heart and naivety she can be perhaps too helpful to the wrong people. That isn't to say she is weak willed. From her experience with Kopii Rezo and Zanaffar she does not shrink away from life-threatening danger in the face of Phibrizzo. Sylphiel also possesses a slight temper but it is rarely seen, as it's nearly impossible to make her angry.
She also has a bit of a wild streak that was shown in her childhood when she stole the Bless Blade and hid it in Flagoon even though she knew it was wrong and would send the city into a panic. Another example was when she was going to try to use sex appeal on Phibrizzo to save Gourry. This shows how much Sylphiel loves those she is close to because even though she is not extremely skilled in battle and can be easily overpowered, she is fearless when her loved ones are in danger. She has a strong determination to protect herself and others, this shown when she mastered the Dragon Slave.
Since her adventures with Lina and co. have come to an end, Sylphiel mainly wants to lead a happy life and help to rebuild her beloved city. She is well prepared to live on her own even though she's lived in Sairaag for most of her life. It's still a desire of hers to marry however and raise a family, possibly because of a fear of being alone for the rest of her life. She is no longer bound by her grief from the fall of Sairaag, since she knows that life goes on and she herself has to as well for the sake of those lost, but they will always have a place in her memory.