So the Crimson Saber only comes in one form because you can only get one of them (at least so far) - it's a reward from the Tower, and to get it to +5 it is actually unique and requires upgrade materials from re-clearing about 2/3 of the Tower.
It is primarily a weapon itemized for Rain's use, that's why it has so much MAG on it, it's probably not good for any of the other greatsword users really