RPG Insanity

how do i unlock the 3rd ending cant really find out how

Using the Completed Game Data, the story tells you, "With a certain item equipped, Happy Ending Route unlocked."  My recollection is that the story makes clear what the "certain item" is.

Does anyone remember which is the certain item needed?

I finished the game, I only need to unlock the third ending.

Advanced thanks.

I don't remember, but looking at my team in my saved game, I'm guessing that it is the "Gold Spirit Armband."  But that is just a guess.

If you still haven't figured out , yes you need to equip that gold armband you got from the extra dungeon from the post match after finishing the normal ending..it will trigger a different solution at the end of the final boss battle.

Edit: done

When you reload your cleared save file, a pillar to the left of the entrance of the sky castle falls over and creates a bridge to a newly available dungeon, where the Gold Spirit Armband is hidden.

This pillar-bridge is NOT shown on the sky castle's mini-map, although you can see it clearly in the sky-castle itself. I usually rely on the mini-map to navigate, so I was confused at first.