In battle 1, character slots 1, 2, 5, 6 will be trapped in the corners unable to move or be chained, so you can only use the characters in slots 3 and 4. In battle 2, two of the corners open up so you can use characters 1, 3, 4, 6, but characters 2 and 5 will still be trapped. In battle 3 and onward, everyone is free. Battle 7 looks like this at the start: So you can position your guys to take out most of the minions at the beginning. Boss is not too bad, but weapon seal can delay the kill for a while if it hits your main damagers.