different legacy item system

So in my setting I have a different way of doing legacy items. Each PC gets there own legacy item and it grows with the character. So at 1st lvl the item will give them a minor benefit like +2 to a skill or if its a weapon then it would be master work. As they grow the item grow to point of being an artifact.

The reason why there are these powerful items is that there was a war of the gods. The gods destroyed there bodies while fighting. In their place were these items. So in other words these items are parts of gods. (sorry if my spelling is horrible)

Example: The Blood Oath Sword it is a +3 keen bastard sword of collision. The wielder must make an oath and can not brake that oath or lose 1d4 lvls. He can turn into a oath demon once a month. Oath demon is a home brew demon that I have made.