Ok it's time to pre-game a bit here make sure your immortals have white magic of some sort on them, Crisis Defense Boost and Crisis Attack Boost. Go N down the path but stay to the E side. In a ruined building you'll find a chest with Sandman's Seals x 5. Continue N and you will see a 2 kids looking at some flowers. Approach them for some scenes and a boss fight (sort of).