FFIX Riddles v2.0

[_yeojina_]

Another one:
I'm a very good weapon that you can have.
Only one can use it.
There is only one that can replace it.
This better weapon is found at a place you visited before.
To find this great weapon, you must use an item.
To find the second-best weapon, you must go to a place for the first time.
The user of this weapon is optimistic and endearing.
What are the names of these two weapons?