Cirno is a fairy, a force of nature. Fairies could be considered manifestations of life itself, except this doesn't apply to Cirno since she's a fairy of ice. Ice halts all semblance of life, making her quite a unique fairy. She is also strong―so strong that she always exudes an aura of coldness around her.
Cirno, the super strong fairy, spends her days freezing the Misty Lake, napping on its frozen surface, and freezing frogs for fun. In other words, she has plenty of time on her hands.
"I wish some big, bad, evil guy would appear..."
Sighing, Cirno looked up at the sky. It was then that she saw a massive shadow rising out of the mist. Was it a giant? A youkai? A god? Or was it the big bad she was hoping for?!
Cirno jumped to her feet and raced toward the shadow. The foe she was waiting for had finally arrived. Unable to contain her excitement, her aura grew colder as she flew through the mist. In extremely cold weather, mist turns into tiny crystals of ice that shine like diamonds in the sky. The water just below her also froze solid, like a carpet of ice rolling out before her.
Cirno tilted her head in confusion as she flew.
"I feel like I'm forgetting something... Oh!"
Slaying evil is a hero's job, and a hero needs a hero's sword. With that simple logic, she created a sword out of ice―the same sword that she claims to have used to defeat a daidarabotchi youkai in the past. It had a small grip to perfectly fit her hand and a big, chunky blade to pulverize her foes. It's actually quite remarkable how Cirno can create ice out of nothing, but she doesn't seem to realize this.
"I'll protect Gensokyo's peace!"
Resting her newly made ice sword on her shoulder, Cirno charged toward the colossal shadow.
"Go get 'em, Cirno!"
A big fairy cheered her on as she swung the sword straight down, bifurcating the shadow in one clean hit. The impact of the blow froze the surrounding mist, creating a shower of diamond dust that fell on the Three Fairies of Light, floating before her.
"Well done, Cirno. You defeated the Brocken Specter!" declared Sunny with a smug grin.
"Brocken...? I feel like I've heard that name before. Whatever. It was no match for me! I protected Gensokyo's peace!"
The fairies continued to play at being heroes for the rest of the day.