It took me a long time and have to dive in the game file to find hints, you might no longer play this game, but here's for people that interested
To open up this damn chest at the beginning, you basically have to finish the whole game... yes the whole game
HOW TO:
1st. You have to clear both of the dungeons that you can see on the map.
2nd. On the second dungeon, you will obtain a hint about a secret in the well next to your house. Go inside the well and while on the rope, face to the right onto a crack, there's a 2nd hint
3rd. Play the game until you got the ability to go to the future. Then, go to the future, there's a new house on the map next to your house. Go inside, and you will find a well on the left side of the house, then go inside the well, and just start clicking on your way down, because there are no visual cues to help you. You will find a button there.
4th. Went back to your house and go inside the well, this time you can go straight down, There're two chests, one of which have a bean.
5th. Went back to the past, open the map, and go to the southeast part of the map. There, you can plant the bean.
Last step. Go to the future, the bean will open up a new dungeon. Clear that dungeon, and voila! You can finally open the chest at the beginning.
You goddamn welcome,
Sincerely NK