My friend just got platinum trophy, he show me the reward garb.
He warned me that not to play hard mode in 2nd playthrough. It's possible to beat aeronite, secret dungeon and etc, but it almost impossible to defeat final boss (in ++ version).
The maximum attack and magic power in this game is 5,000. He has modified some weapon to reach that point, but still can't defeat final boss. He think that may be we need to play again and gain until HP reach 99,999. But we won't do that.