Tiffania was referred to as a forest fairy by Louise and Saito. Living in shadows, Tiffania helped out many strangers in the forest, including Saito, and possibly Guiche (according to one of Guiche's stories).
However, in the light novels, Saito does ask himself if the nourishment from her body moved to her chest. Also, there were only three letters he could think of when he first saw Tiffania accidentally land on his lap.
Louise, as well as Siesta, feel jealous whenever Saito casually talks with Tiffania, as if he was making a move on her. This was because, when Saito returned to Tristain, bringing Tiffania with him and Louise, he said to her "I will protect you," something he also told Louise which Louise feels comfortable with, until that time. Unlike Saito's promise to Louise, though, which was because he truly loved her, Saito's promise, "I will protect you." to Tiffania was only due to eternal gratitude for resurrecting him, but Louise does not see this.
In the Light Novel, it was confirmed that Tiffania was a Void User, she was the Void User from Albion. However, in the anime, she refuses to reveal her childhood which she terribly does not want to remember. Also, Louise hints that fact when Sheffield asks for the "other Void user.", although she absolutely refuses to accept it because of Tiffania's kind personality, beautiful form and nice tone, she has no chance of winning Saito's heart. Despite all of this, she can (naively) ask Louise is she and Saito are lovers.
Although Tiffania likes Saito, it is not to the point of actually having true feelings for him, it is more like a close friendship because Saito was the first human of her age to accept her even if she was an elf and was not afraid of her (Elves were despised in Halkegenia at that time, until Tiffania's origins were revealed in the Academy and she makes friends after kindly forgiving the (previously) arrogant Beatrice despite the belief of elves showing no mercy to humans). In the Sleipnir Ball, she masquerades as Saito; Louise thought the one she saw was Saito, but looking a bit down, she saw a huge chest, because the magic did not seem to remove Tiffania's chest size, so she looks like a Saito with huge breasts. Upon arriving at the Academy, only Saito, Louise and the Ordine Knights knew that Tifa was a Half-Elf and agreed to keep it secret under the Princess's orders. But because she revealed her true roots, a jealous Beatrice chose to give herself a fake title of Bishop and gave Tiffania heresy inquiry, which required Tifa to step into a boiling pot of water.
Saito purposely begged to Beatrice for Tiffania's sake (and Louise, because she would be in trouble), but Beatrice refused and Tiffania told the latter that she was still a child, which enraged Beatrice even more. Then Saito drew his sword, and fought Beatrice's bodyguards. A then angry Louise (who was having a dream of her and Saito happily playing around a meadow shattered because of the noise) proceeded to make the whole battlefield explode. An already furious Beatrice snapped at Louise, while Louise calmly replied that only the Pope of Romalia can give the title of Bishop to someone else.
This embarrassment led Beatrice to beg for mercy at Tiffania's knees, but the latter just warmly hugged the crying Beatrice saying that she only wanted to make friends, not enemies. This incident led to Tifa having more suitors and more friends, but still keeps Saito and Louise as her closest friends.
In Volume 19, she was kidnapped by the elves sent to capture Saito as she arrived at his mansion to prepare to summon her own familiar, as they are interested in why there is a half-elf with Saito. The elves eventually found out Tiffania was a Void magic user and decided to give both her and Saito the same drug Tabitha's mother took in to make them lose their mind in order to incapacitate the human's assault on the elves. Saito and Tifa were rescued by one of the elves that was sent to capture them due to her own interest in finding out more about Saito's home world.
As Saito and Tifa fled they was stopped by the fiance of the elf that freed them. As Saito fought he was hit by a sleeping spell, and on the verge of sleep Tifa was told by Derflinger to flash Saito to wake him up. Tifa obliged without realising the consequence at the time, and was very embarrassed afterwards. Thanks to Tifa's help Saito overwhelmed the elf opposing them and managed to escape from the elves' Capital city safely.
In season four, Tiffania is told she is a void user by the Pope of Romalia, and is soon given the ring of Albion by Queen Henrietta. Henrietta states that since Tiffania is the last of Albion Royalty she is the true owner of the ring. Later Colbert-Sensei teaches Tiffania the familiar summoning spell, while doing so Saito appears from the gate this coincides with the light novels that Saito is a familiar to two void users. Also, her confused feelings for Saito are realized during the end of the first episode.