Lily, also known as Flechette, was a member of the New York Wards. Following Leviathan's attack on Brockton Bay, she was transferred to the Brockton Bay Wards. She eventually left the Brockton Bay Wards and joined the Undersiders under the codename Foil.
She initially hoped she could become friends with Shadow Stalker, the only other female Ward her age in Brockton Bay. She noted that her work would "drain the life out of her if she had no friends to do it with". However, she was shocked by how comfortable with violence Shadow Stalker was. Later, she professed that she was never good with the ick-factor of the job.
She kept to an exercise regimen, and spent four nights a week in the gym.
Lily was a lesbian, and was immediately attracted to Parian when they met. She was willing to risk getting into trouble with the Wards in order to befriend her.
Lily is described as a Japanese-American girl, of above average height.
As Flechette, she wore a skintight, deep purple costume with a visor, quiver, and narrow platinum-white armor panels that flared out at the upper edges and tapered at the bottom - mimicking the vague shape of an arrow or darts. Her costume included metal cleats on her shoes, that could dig into the environment under the influence of her power, or help her grasp the chains her arbalest launched.
She carried a Tinker-made arbalest to launch needles three feet long – needles that carry the effects of her power, ignore gravity, and benefited from her secondary power of enhanced sense of angles and timing. The arbalest produced an unlimited supply of sturdy chain, and her needles remained fused in place where they hit, allowing her to use it as a grappling hook as well as a weapon. She also carried nine-inch throwing darts, her primary weapon before she acquired the arbalest.
After Lily became Foil, she donned a black costume with asymmetrical belts, boots, armor and gloves. She also wore a black opaque mask with silver trim at the edges. As a weapon, she used thrown blades augmented with a rapier, the same tools she originally used when she first discovered her powers.
Lily has the ability to temporarily imbue nonliving material with the power to ignore select laws of physics. Most notably, they could punch through anything. She is not restricted to her hand when she uses this power. If her power wore off while an object was moving through another, it would be stuck in place. She could use her ability on her costume to reduce the effects of friction or make her shoes bite into surfaces. Another trick she could do was to make her costume frictionless and allow her to move around.
Scion described her power as "charging objects with energy [...] the small pieces of alloyed metal unfolded, taking shape in not just this world, but all realities, at the same space and time, bristling with an effect that would sever their attachment to most physical laws." Although this is widely interpreted to mean that they extend into every Alternate Earth, this may not be the case.
Her power is ineffective against abilities that redirect her shots before they make contact.
Lily also has an intuitive understanding of angles, trajectories and an enhanced sense of timing that she uses for aiming and applying her power. It also gave her a defensive advantage being able to dodge blows easily and even catch arrows out of the air.
Foil can destroy an Endbringer's core if it is exposed. However, once the sheer amount of damage she could do to Endbringers was realized after the Battle against Behemoth, the Endbringers changed their tactics.
Using her power on Chevalier's sword would have broken it, This is due to the fact that Flechette'a ability to warp space beat Chevalier's, much like the Endbringer's core was able to withstand Chevalier's ability. It caused the Siberian to flicker and vanish on contact, and Lily would have had a similar effect on Clockblocker's field.
The Entities referred to her power as "Sting". It was originally used for fighting other Entities. They haven't found a way to improve it for aeons, but it was still useful to see how other powers interacted with it.
Lily was put into the foster system at a young age, and had older siblings who weren't.
She triggered 3 years prior to the start of Worm, as part of a group trigger in New York. This trigger event occurred when she was standing at a subway platform. She was attacked from behind by one of her estranged sisters, who was homeless. Her sister tried to push her onto the tracks and in the process, other people fell onto them. Lily triggered as her sister pushed her head down, putting it in the way of oncoming trains, and seeing her sister get hit. One of her old nemeses, March, was another part of that group trigger.
Has settled into a routine as Parian's lieutenant. while preparing to deal with a hostage situation she caught up with some of her old Ward teammates. She had takien to imbuing a dagger with her effect and letting Parian incorporate it into her creations, like a fluffy scorpion.
During her battle against Scion, Khepri noticed that he was dodging shots from Foil. When he gave up hope, Foil was able to wound him, opening a hole to his true body through which he was destroyed.
↑ 1.01.1Foil is 17 and a senior. She triggered 3 years prior to her appearance, as part of a group trigger in New York. One of her old nemeses, March, was another part of that group trigger. - Wildbow, archived on Spacebattles
↑ 2.02.12.22.22.214.171.124.7Flechette wasn’t a breaker, though her power came close. Technically, she was a striker, a cape with the ability to apply some effect by touch or at point-blank range. The striker classification could include certain breaker effects as they were applied to things other than the cape themselves, but not always. Other strikers included those who used energy weapons, those who had certain kinds of superstrength that weren’t accompanied by durability and those with pyrokinesis or such that didn’t extend more than a foot around them. The way she used her ability, coupled with the intuitive understanding of angles, trajectories and timing she got from her secondary powers, gave her a low rating as a ‘blaster’. A cape with a ranged attack.
She infused the three-foot length of sharpened metal that was mounted in her arbalest with her power. The more power there was in it, the less it was affected by the natural laws of the universe. Focusing more power into an object meant gravity, air resistance and general physics held less and less sway over it. She could tune it, make the effect longer lived, shorter lived or bias the effects to allow for more of one element or less of another.
She could do other things, but the primary benefit, the easiest thing to do, was making her ammunition punch through anything. It would glue itself in place on impact, if she had the effect wear off at the right time, and she was very good at timing things. She could charge the metal of her cleats so they bit into any surface, and though it was too slow to be used defensively unless her foe telegraphed their attacks, she could make her costume frictionless. - Excerpt from Sentinel 9.2
↑She bounced between her mother, her father and the surrogate mother who had attempted to renege on the deal they’d made and keep her. - Excerpt from Cell 22.3
↑“I”m not good with the ick,” Foil said. “The Dolltown victims were almost too much for me. Parian knows. I’d always prefer riding Parian’s dolls instead of Bitch’s dogs.” - Excerpt from Blinding 11.6
↑ 6.06.1Parian was rescued by one of the out-of-town Wards, a girl in a skintight costume with a visor covering her eyes, nose and ears, with a quiver of what looked like giant needles and a massive crossbow.
"Flechette! I'm getting closer!" Shadow Stalker called out, looking back at her new partner.
"Careful!" the crossbow-girl – Flechette, I took it – replied, loading another shot.
↑ 7.07.1 A Japanese-American girl, she wears a deep purple costume with a visor, quiver, and narrow, platinum-white armor panels that flare out at the upper edges and taper at the bottom – mimicking the vague shape of an arrow or darts. - 
↑Flechette, now Foil, stood off to one side. She’d donned a black costume, which I was pretty sure was made of one of my failed attempts at a Tattletale costume, using asymmetrical belts, boots, armor and gloves to cover the areas where I’d tried to embellish. Her mask was an opaque pane, like Clockblocker’s, but black, with silver trim at the edges. - Excerpt from Drone 23.5
↑I would have locked my eyes to hers to read her expression, but she wore a fencer-style opaque pane that covered her face. Her costume was form-fitting, sleek and stylish because of course it had to be when she was partnered with a fashion designer, but that costume was normally adorned with a fanned-out array of spikes where the javelin-like bolts were in her quiver, darts mounted at her forearms, hips and thighs where she could grab them. Most were empty now. - Excerpt from Blinding 11.8
↑Thirty might be too generous. Look at Brockton Bay’s Protectorate/Wards, living or dead. Who is explicitly affected by the (conventional interpretation of the) Manton effect? [...] Flechette? Yes. - Comment by Wildbow in Plague 12.6
↑Flechette moved to shoot, then reconsidered, threw a handful of darts at Trickster instead. The darts disappeared in midair, and splinters of wood and small stones dropped straight out of the air where they had been. - Sentinel 9.3
↑ 18.018.1Using her power on Chevalier's sword would have broken it, like the space warping around the Endbringer core did. The issue was that after they discovered the full ramifications of her powers, the Endbringers changed their methodology. Leviathan made hit and run attacks that meant he was gone and attacking another city before Scion/Foil/anyone else reached a location, Simurgh attacked abstract targets, Khonsu teleported, and Tohu/Bohu were difficult to pin down or find easy answers to. - Comment by Wildbow on Reddit
↑Sting, for the record, is akin to the shark. Sharks haven't evolved for aeons, because you can't get much better than a motherfucking shark. What you can do is put the shark in a tank with other fish/animals and see the way things might play out. - Wildbow on Spacebattles
↑“I was fostered, entered into the system. I had older siblings who weren’t. Subway platform in New York, I get attacked from behind, and it was one of my sisters, homeless, and so- so angry. It was like she lived in a completely different, warped reality, where I was to blame for everything, I’d sold her out, I’d taken something she was owed. She tried to push me but I caught myself, and when she tried again, she pushed other people down onto the tracks while pushing me down to the ground, put my head in the way of any incoming trains.”
“March was one of those people on the tracks?” I asked. “Her timing power… and an imminent train?”
Foil shrugged. “All I know is I triggered as the train hit my sister, convinced she’d killed me. March says our third was a friend of my sister, but I barely met the woman, and I didn’t realize why she was important or what she meant when I did.” from Blinding 11.10
↑In the moment that hope died, the girl with the injured hand used her power on the iron rods. Infused them with the energy he was afraid of.
I discovered why he was concerned about the power.
It kept things from being contained. I got a glimpse, a flash of a look into the world beyond him, a world he’d shut off, to which his body was the only conduit. - Excerpts from Speck 30.6. "The girl with the injured hand" refers to Foil.