There are plenty of other moves which a powerful which only last one fight.
The other way 'around' the no one would just run into the mirrors, is
At the end of the battle it says, 'Your mirrors melt away' Then at the start of the next battle it could say 'You reform your mirrors around ____.'
This could be like when Gaara had his chakra enriched sand, once he had put his chakra in it, it took little to no effort for him to use it, so the same could happen with the mirrors, once you've frozen the water to make them and put your chakra in them, then maybe it would be easy enough just to reform them.
Hate to jump in the middle of a topic but how about this?
Haku in the anime could make mirrors easily but maintaining them was an issue, how about making the mirrors start out with a stat of 100 hp and 50 Atk + what ever small stat boost to speed or dex. Then make it so the mirrors degrade over time and last without any outside influence about 4 turns before they melt and finally crumble?
I guess what I am saying is:
100 hp and 50 Atk + what ever small stat boost to speed or dex + with a one quarter stat and hp reduction over 4 rounds until they become ineffective and disappear.
Also maybe a little move you could add is to spend about 1 chakra per mirror to maintain them just like you can heal companions.
Mirrors will have no attack, they can only defend, and I don't think they should healable, or only last so many round, I think they should last until they are destroy, or end of fight like Neji said.