Here's how to prevent your weak characters from dying.

If Ike is the commander, simply do not let your weaker allies attack by taking them out of the battle using the Units screen. Just select the people you don't want to get hurt and hit the A button.

This does not work with characters highlighted in green. This means the Ike cannot EVER be recalled and in few instances, neither can Elincia or Ena.

If there is no way to recall a character from a battle, there is a way to make sure they never get hit.

All you have to do is click on your enemies with the A button and it will show you their attack range. Make sure to do this with all enemies or any enemies that are relatively close. Of course, you will not need to do this with enemy soldiers who are on the opposite side of the screen, but it is wise to just double check.

Also, check the attack range of any and all magic users. They could pull a meteor or blizzard attack (which have ranges of up to 10 spaces.) Have a stronger unit go ahead and take care of any close by enemies, making sure all allied unit that you want to protect are out of the enemies' attack range.

Repeat the enemy target check for the next turn and move your allied units who you want to protect closer, still keeping them out of the target area. Keep clearing out the enemies who are close so you can keep progressing without your protected allied units taking damage.

Also, if you can't seem to get to the magic user who is using meteor and far range magic attacks like that, send a unit with a high resistance to magic into the target zone so that the usage of those deadly magic attacks can be used up and you're safe to keep moving on. Good luck, fellow gamers!