I like it :]
The art style/running reminds me of tales of phantasia for some reason (and I loved the game). Anyway, I see a lot of people saying the only way to kill a dragon is with the Divine Edge, which is not completely true, especially for the first couple times you run into one - having an elixir and just a couple upgrades into your weapon allows you to auto attack it to death. For me, that's normally how I killed the dragons I met before around day 20.
And to KowSakujo - you should always have enough money for armor - I hardly ever upgraded my weapons past 2 or 3 times before day 10 because I always saved money for armor as my secondary heal but also mostly for the chance to get the gold voucher, which costs 500. I can pretty much always get the voucher before I see my first dragon, which makes upgrading every weapon option (and getting an elixir or Divine Edge) you see before that time for a while a no-brainer.
Anyway, back on topic. When I first saw your question "Have you ever wondered how will an RPG be played if it uses only one button?" I immediately thought of Super PSTW Action RPG which made me wonder if this was another troll game, but nope! Thanks for opening my eyes, because I HAVE asked myself that before.