Let's Play Genius of Sappheiros (Extra) Part 2
Many of the quests will take you back to areas you have already been. Character quests will give you a message when you are in the section that has the character. You can just clear out the area until you find her or just constantly run from fights until you find the boss. You can also run away from the boss fight and try again if necessary. If you are fighting new enemies, you are in the correct general area of the dungeon for the quest.
Also all Character quests will add 3-4 chests to the area for you to loot.
Cirno:
Easiest of the character bosses. She uses ice attacks and will eventually gain some regen from water land effects. Just spam Lithos's multi hit attack and you will be just fine.
Cirno (character):
Mostly a gimmick character. Cirno is a mage specialized in ice magic that has a chance to cause Freeze. She also has a few Instant Death attacks. She has a few nifty abilities like self target reflection and the ability to counter spells with ice attacks. Unfortunately, most of her benefits are extremely limited.