Sylphiette/Chronology

Mushoku Tensei Novel Volume 1 - Infancy Period
Sylphiette is first seen being bullied for her emerald green hair and getting chased and getting hit by mud balls thrown at her by the village children, Rudeus saw the event and decided to step in to stop the bullies. After chasing them away he then proceeded to wash the mud off her with warm water he made using magic. She was particularly attached to Rudeus and could not bear to be apart from him.

Mushoku Tensei Novel Volume 7 - Youth Period - School Entry Chapter
She is reunited with Rudeus at the Ranoa Magic Academy, however he did not recognize her because she was disguised as a boy and her hair had turned white as a result of overusing her magic during the Mana Calamity. Then, she was disguised as Fitts-senpai and the bodyguard of Ariel Anemoi Asura.

She is known as the [Mystery], the one who was feared between Ariel, Luke and herself. It was said that she had once single-handedly managed a handful of delinquents that posed a threat against Ariel, which caused people to stay away from her.

In the volume, she had been the one to test Rudeus to see if he was truly eligible as a [Special Student] of the Ranoa Magic Academy. She had later been shocked by how strong and potent he had become, even though he had only displayed the skill [Rock Bullet].

She is often seen in the library and had many meet-ups with Rudeus there. At the Magic Academy, like Rudeus, she had made use of it to find the reasons behind the Metastasis Event, even aiding Rudeus to find out the cause of it. In fact, she even remembers the titles of the books that she has read, showing her intellectual side.

For the most part of the chapter, she is seen trying to make Rudeus remember who she was, as she still held a liking for him. In the end, she helps Rudeus cure his impotency and she becomes his wife.

Before the happenings of the entry into the Magic Academy, she had been teleported to the Asura Kingdom and found herself falling from the sky. In a desperate attempt to soften the blow she cast magic one after another which caused a mana strain, causing her hair to go white. She then coincidentally lands into the place where Ariel was nearly assassinated by a rampaging magical creature and saves her by throwing out a spell.

The incident earns her recognition and she is later promoted to become Ariel's guard, escorting and protecting Ariel until the end of the Asura Kingdom Arc and Ghyslaine Dedorudia takes over her role.

Mushoku Tensei Novel Volume 20.5 - Intermission Chapter
Sylphy is pregnant with her second child.