Head on back up to Camlon and speak to the king's adviser. He suggests going to Winlan, which is east of Camlon. You'll have to pass through the ruins of Nanai to do so.
You'll want to sort your inventory manually to help you in fights. It's best to keep healing and AoE items up near the top, so they can be reached fast. Specialty items, like Fire Stones or Acorns, can be lower in the order. Keep any items with a non battle use toward the bottom. Once you gain access to the bank, this will be easier to manage.
Along the way to Winlan, you may notice this symbol on the ground. This is a dragon mark, and it shows the location of buried treasures. Much later, you'll get Mogu, who can dig on the map screen and collect those treasures for you.
You should only need to carry around 3 stacks of Herbs, and 2 stacks each of Antidote and Tear Drops. Keep at least a couple of Lives on you, and stock up on Acorns at the shop. Once you've done all that, store your left over cash and back into town. Don't bother buying anything at the weapon shop. You'll be finding some nice stuff soon enough.
Speak to the woman by the door to advance the story. She will tell you to wait in the lobby after you ask about speaking to the King.
Her spells are Cura, Fort and Heal. Cura restores around 50 HP, Fort increases Defense, and Heal clears most status effects, like Poison and Zombie.
You'll notice she doesn't have a shield or helmet. You could have purchased some way back at Drogen, but there isn't a need to. We'll be finding some stuff in the castle in a moment.
Talk to Nina's dad to get an idea of how bad the situation is.
Head out of this room and down past the two fountains to reach a set of closed doors. Use the action button in front to open them and you'll find four chests ripe for the picking.
Head downstairs and to the west to find a room with two chests in it. After you finish getting sloshed, open them up.
Head on out of the castle and into Winlan proper to start your journey for the Remedy.
See you then, thanks for reading.