Yea I'm way early game, here is what I have, I only have the two five stars. I summoned a couple red guys for diversity afterwords cause I was bored of blue and greens.
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Ok.. Eirika is a much stronger red to swap in and level up. ..
Go to training sanctum and train up Eirika right away up to level 10+ to match ur other team members, it should be pretty fast only take a few minutes..
When training her, use her to kill everything to get all the xp..
Look for green units on the training sanctum (it lists the units you will fight) pick the one slightly above your character's current level.. so eirika can train on the 1st or 2nd sanctum starting out..
Bring shareena with you to train with eirika using shareena's +4 attack buff can really speed up training, because it will allow eirika to outclass the equivalent leveled opponents.
if she has color advantage she can train 3-5 levels above her..
Consider pulling 1x 5s green off the wyvern flyer banner, if you do that.. you will have to train up your shareena and eventually promote her to 5star.
because shareena can take hits, and will really punish other reds at 5 stars.
The game changes significantly at end game level 40s, the characters all then have very specific tasks..