You don't have to kill Kishuana in the turn he appears. You have to kill him in one turn. First, kill everyone, especially Aion except the morphs. The trick here is that you should have arena leveled your units. Once Aion is killed, line in your Pegasus knights on the mountain away from Sinper's attack range. Place Hector on the gate but DO NOT SEIZE THE GATE.Then, line in charaters with support bonuses (people with +10 hit and critical etc) and Use Oswin to kill off the first knight. Then, attack Kishuana with Lyn with Mani Katti. If you are lucky, Lyn will execute a critical. Send in a Pegasus to rescue Lyn. I sent in Guy next(promoted and with Silver sword) if you are lucky, they will perform another critical. Then if Kishuana survives, send in a Pegsus knight to rescue your unit. Then send in Eliwood with Rapier. If your are sucessful, another critical. Then, use bow units to finish him. (I used Lyn, Guy, Eliwood, Bartre and Rebecca). Once dead, seize the gate immediately. You don;t want snipers to chase you, don't you?
As for teh spoiler, Nils and Ninian's father is...Nergal. (DUNDUNDUN)
