Finished Ice event mission on 2nd try. Failed first on level 1 because I didn't notice it was timed. Did not notice anything removed after a loss (noticed arrows disappearing when starting new girls). Reward for winning was Bra (+50% to second stat), Panties (+13% to all stats) and full-window animation sequence. I just wish the scene was unlocked in a way that you can access it anytime even after event is finished.
Completed some more girls:
Ice: Bra (+50% to 2nd stat), Panties (+13% to all stats)
Geeky: Lingerie (+35% to all stats)
Dora: Lingerie (+30% to all stats)
Frecly: Lingerie (+42% to all stats)
Pantress: Lingerie (+35% to all stats)
Victoria: Bra (+25% to all stats), Panties (+16% to all stats)
You can also see an animation by using a link https://nut.fakelay.com/girlownanim/<number>/ where <number> is 1-17 for different girls. But this link only works if you have finished a mission for that girl else you will see an empty room, so is kinda useless if you want to cheat and see a scene without completing a mission. Can be useful to access scenes after event unless it is removed.
Edit: finished all my arrows, will do remaining 3 girls after 21+ hours.