Help Identify: 2-player Kingdom building Board Game with role selection
After doing some searching on BGG, I think it's Greedy Kingdoms by Japon Brand. AEG mentioned in 2013 that they plan to release it, but I don't believe there's been further news of a Western release. The game was restyled and included in the Princess Wonder game collection. The English rules can be found here.

As you say, the game is won by building two "Royal Palace" upgrades. There are four resource types: gold, food, honor and land.

Each turn, the current player is the attacker. They may build an upgrade (from the four face-up which replenish, or the pile of three Royal Palaces) or buy a special worker, which replaces and upgrades a basic worker from their hand of eight.

They then battle, secretly selecting three of their eight characters while the defender does the same. The attacker must pay the costs of any matched cards but gains none of their benefits. They then play their unmatched cards, paying the costs and gaining the income.