The game cannot be completed in one playthrough because of the weapons. Syriu, the girl blacksmith in Selray, will have three missions for you that will give you weapons for three characters; later in the game, she will make three Sun Stone weapons (since only three Sun Stones are available in the game). You will have to get the ones you missed on a second playthrough.
Also, it's very easy to miss the wreaths you get from Rilche, the little girl with the lisp in Selray. Very late in the game, she will ask you to bring her three flowers (this will be on the quest board). Instead, be sure to give her three of each; she will then give you four wreaths, all of which are considered accessories.