You should worry about the S rank item from Haruna. The enemies' average level is 22-23. Focus on that S rank item in case you don't have it yet. It's a useful item, the best one for a mage.
Then, and I agree to Antimatzist, the chest and dig items from the elemental chambers are more useful than their S rank items, so get the latter later.
No matter if you're attempting S rank or not, try this:
- Use only water characters in Flowing chamber. Equip salads. Yu can be useful here. Else use Lalacle, Wendel, Mizuki, Corselia, Flare, Sigurd, and maybe Mercenary Leader or Simeon. And Noah, but not for S rank.
- Use mostly wind characters in Cyclone chamber. From my memory, I'd say Cyclone is the easiest chamber. Use Lazlo, Kika, Nalleo, Dario (but only with a Windspun Armor), Seneca + Andarc, Ameria, Roget, Paula. And Noah, but not for S rank.
- Not enough good lightning characters, so use a mixed party in Thunder chamber, but maybe no water characters. Ornela + Busk, Kate, Andarc + Seneca, Jeremy + Millay + Trishtan, Akagi, Nalkul, Champo, Frederica, Yellow Mercenary, ... And Noah, but not for S rank.
"Within the four seas, all men are brothers" Shuihu Zhuan