The theme is horrendous, worst in LD history: "It's Dangerous To Go Alone, Take This". My ideas currently look like this:
IDEA #1 - Scuba Jim
Dive for pearls. Trade them for diving supplies. Scuba tanks let you swim deeper and longer, harpoons kill sharks, lucky charms make oysters more likely to contain pearls. Keep going until you die or become too rich to continue diving and end up as a boring rich person.
IDEA #2 - Shopkeeper Jim
3 parts. Commodity store where you buy wood, metal, etc. Crafting interface ripped straight out of Minecraft, where you build that into RPG items. And finally, storefront where you sell the items to adventurers.
Tension: you want to charge lots to make lots of money, but if you charge less, adventurers will buy more and be better equipped, thus living to return to buy more.
Simulates the adventures.
IDEA #3 - Petstore Jim
It's dangerous to go through life alone, and the #1 killer in the USA is heart disease. Petting an animal reduces your blood pressure. Ergo, buy a pet.
IDEA #4 - Roguelike Jim
Roguelike because roguelikes are fun.