No-one ever found Letty Whiterock when she did not want to be found. It was to the extreme that people belived she only existed during the winter.
Of course, this wasn't true. However, she was so weak and vulnerable during other periods of the year, that she would simply return to her home. Her home in the Gensokyo Mountain Range. No-one ever went there, they assumed no-one lived there, but Letty did for nine months of the year, sleeping for eighteen hours each day, only active three hours each side of midnight, when it was coldest.
The same location was where she usually went to teach Cirno. The snow fell heaviest on these mountain ranges, the the temperature was the lowest year-round.
However, over the past year. Letty's had spent what power she had, and her time awake, investigating. She had discovered that someone else was in the mountains, with ill intentions, intentions that would bring chaos to Gensokyo. When winter rolled around, Letty found out what her objective was, and that danger to Gensokyo was immiment.
Strong as she was [Although very bad at danmaku simply for lack of practice], she knew she would need help, and that Cirno would inevitably tag along anyway.
"Letty! Can we make snowmen!" Cirno yelled, snapping Letty out of her thought.
Letty smiled at Cirno, her smile far warmer than one would expect of the Yuki-Onna. "Sorry Cirno. Not today. Today I need to teach you something. You see, I've been thinking about your weakness."
"I have a weakness?" Cirno asked.
"How many times have people stood right in front of you in your spellcards and just chanted 'baka'?" Letty said.
Cirno's eyes shifted around, from side to side. "Neeever..." she said, like a child that was obviously lying.
Letty sighed. "So you don't want to learn something useful?"
"No, no, I wanna learn! I just wanna play first!" Cirno said.
"Cirno, you have to learn this today. You see, something is going to happen soon, and I'll need you to be stronger to help me." Letty explained. She didn't want Cirno to worry about everyone else, so didn't tell her what was happening.
Cirno sat on the snow, and just started making a snowball.
"OK~" Cirno said, before she threw the snowball at Letty, a mischievous grin on her face.
Usually, Letty would let Cirno's pranks, however obvious, work on her. Her usual 'surprise snowball' was no exception. This time, however, the Yuki-Onna used it as an example.
"Ice Breaker..." she murmured, before she raised her right arm, the snowball cut in half.
"Eh?" Cirno said, looking confused. Letty was holding a large chunk of ice, shaped like a Claymore. Despite it's size, she held it one-handed.
"I want to teach you how to make up for your weakness at close range, and a way to get through defenses. You see, something you are holding made of ice is a lot tougher than a projectile. You can also control it's shape a lot more, it can be far sharper." Letty explained. "Attack me with a huge chunk of ice, big as you can." she commanded.
"Attack you?" Cirno said.
"I want to prove it." Letty said. "I'll cut through the ice before it even hits me with this."
"OK..." Cirno said, as she formed a large chunk of ice, twice as big as her, above her head, before hurling it at Letty, using her Ice Manipulation to control it, instead of her raw power.
The chink of ice, as large as Letty, rushed towards her, and the Yuki-Onna calmly swung her Claymore, slicing it in two, without the slightest chip on her weapon.
Letty looked at the sliced ice, and noticed it was significantly more than Cirno could make last time she did that.
'It won't be that long now. I remember what she told be when the Yama warned her. It can't be much longer, until she Transcends' the Yuki-Onna thought to herself. She knew some legends of old times, times before her, that her mother had told her oh so many years ago, that she wanted to test.
She looked at Cirno, and noticed she was already collecting ice in her hand, focus etched onto her face. It wasn't normal for Cirno to be that quick to try new things... but Letty did not expect what happened next.
Usually, when someone attempted to form an Ice Weapon for the first time, they instead froze their own hand. While as a manifestation of cold in nature, Cirno learnt far quicker than Letty herself had, she did not expect Cirno to form an icicle, vaguely like a dagger, as well as managing to freeze her own hand.
The Ice fairy then swung the dagger at Letty's own weapon, and the dagger shattered, like her ice before. That was predictable, since the ice was transparent, not an almost opaque blue, from the sheer concentration.
But it was faster progress than expected.
Cirno tried again, and this time, the dagger was larger, and there was less ice on her hand. She looked tired, but kept trying.
"Remember Cirno, something like what I have will be too big for you, make something smaller." Letty said.
"Oh... yeah."
"The ice has to be dense too. Like the ice under snow that has been trampled on, except much, much thicker. The denser the better." Letty said.
Cirno tried once more, her hand not freezing, and the dagger-like icicle getting larger and darker. This time, a small, tiny chip was made in Letty's weapon, which she quickly repaired.
Two hours passed, and Cirno had managed to make a proper dagger in one, but spent the remaining hour trying other weapons, to try and find one she felt comfortable with. In the end, despite using a hammer quite a bit, Cirno decided she liked a thin-looking short-sword the best, probobly since it was light enough for her to swing around properly. The weapon wasn't as strong as Letty's, and shattered on impact, but left quite a mark, and probobly would never not break first, simply due to the weight difference of the ice.
The ice fairy was resting, when Letty felt disturbances in the snowfall. A large group had reached the suspicious area. There was the clear shape of a broom, meaning Marisa was amoung the group.
"Cirno, get ready. My training about how to make that weapon wasn't just about the weapon. You should be able to make your projectiles denser too now, although not as dense as the weapon." Letty said.
Cirno formed an icicle, and bashed it into the ground a few times, before it broke.
"Yes, my ice is tougher!" Cirno said.
'We just need to wait for the right time. I only hope we're not even needed, and they stop her before her weapon is finished.' Letty thought, keeping a vigil.
Author Notes: This part was heavily inspired by Advent Cirno, but the concept of weapons made of ice to compensate for Cirno's 'Blind Spot' in her favorite attack makes a lot of sense too.
Letty's a lot stronger than a Stage 1 boss. Part of the reason for handwaved as 'She dosen't practise danmaku', but also remember the winter in PCB was a 'false' winter, longer than it should have been. [Likewise, it's reasonable to assume Lilly was weaker than normal since it was Winter, not Spring, even when it should have been Spring... and Lilly White was already technically the strongest fairy if you look at stage assignment alone.]