Pseudo-NPC, unlikely to actually show up. But relevant to the knights' background:

[list][*][u][b]Name[/b][/u]: (Former) Knight-Witch Merilia
[*][u][b]Age[/b][/u]: 300+
[*][u][b]Gender[/b][/u]: Female
[*][u][b]Race[/b][/u]: Human?
[*][hider=Appearance][img]http://safebooru.org//images/513/5a35aab857a803b1f9af987a979e6a6e6aa47987.jpg?1046052[/img]
The shortest of the original Iron Rose Knights, and possibly the shortest overall, she seems to have stopped actually getting taller at about the age of 8 and a lofty 4'2. Magic was apparently involved.[/hider]
[*][u][b]Personality[/b][/u]: Despite her lack of emotion, Merilia definitely had--and continues to have--a thing for screwing with people, particularly using magic to play tricks. If nobody else is around, then she's likely to practice the pranks on [i]herself[/i], except for the nasty ones. Those all get directed to people that actually thought to mention, or draw attention to, her height.
Most often, her activities as part of the knights were of a scholarly nature--aside from providing magical backup, she would catalogue any magic or strange creatures they encountered, research or design any counters needed, and so on--and she was quite happy to do this, as it expanded her own knowledge. Her lack of interest in the propriety of this knowledge didn't endear her to many people outside the knights, or many within it.
Outside of the context of tricking people, Merilia is never particularly personable and generally keeps to herself. Even then, unless saying something is absolutely necessary, she inevitably communicates non-verbally or in writing. Almost every word the knights ever heard her speak was inevitably the casting of some sort of spell and she was extremely quiet even [i]then[/i].
[*][u][b]Brief Backstory[/b][/u]: As a child, Merilia was raised by her Ithillane mother and followed in her family's magical tradition, including a highly circumspect and definitely illegal (to have a child perform) ritual to maximise mana potential. This had the side effect of prematurely limiting her growth, though nobody can claim that the results weren't effective. 
The adult Merilia decided to not live her life out as a peasant farmer that simply happened to have witchcraft, and headed to the Mage Colleges until she found one that would actually accept her despite the informal magical background she came from. It was here that she picked up more dangerous magic and means to protect herself, even teaching classes for years before again getting bored with her sedentary lifestyle. She spent time as a wandering adventurer, before joining various military companies in Thaln, simply because it was a college there that had accepted her in the first place.
Then the Iron Rose Knights were founded and she volunteered her services as magical support. After Elionne left, Merilia stuck around for just over ten years before bowing out to go exploring again. In the years since, she's sent the knights a letter monthly along with some magical trinket she's found or made, but it's never been clear what she's doing or how she's managed to stay alive this long. With her interest in all forms of magic, someone inevitably proposes necromancy but even when they have the time to spare to try and find her, she's always gone by the time they reach her last sighting.
That the sightings involve dungeons at the best and ambiguously justified deaths at the worst, it's a mystery that someone wants to answer.
[*][u][b]Equipment[/b][/u]: Her wand. It does absolutely nothing on its own, but it can hold a spell to release on command. 
[*][u][b]Skills[/b][/u]: Out of being a mage, Merilia was one of two artists in the early knights, and a lot of her sketches and paintings have been preserved and kept around over the years, though she  tended to depict their battles or the locations they went rather than the knights themselves.
As a mage, her skill-set is large due to her lifetime of changing positions and she has a firm knowledge of many different areas of magic. With the knights, she actually owned no armour or weapons--she'd temporarily conjure them whenever needed, and usually kept the wand charged with 'summon armour' in case of an unexpected battle. In combat, she had a clear preference for using large-scale air spells to compliment the knights' fighting and force the enemy into unfavourable arrangements, as well as to raise her to a height that she had a good view (and avoid the inevitable death-by-arrows you'd expect). This sometimes extended to actually cutting people with the air itself... or making a vacuum blade for particularly messy deaths.
She seems to be one of the few mages capable of long-distance teleportation. It would go a long way to explaining why nobody can catch up to her, and also how the letters keep appearing on the captain's desk exactly at midday on the first of the month. 
[/list]