Help with a player's weapon

[Keeper216]

So one of my players wanted a weapon. She is a level 8 antipaladin fetchling. So the party helped her track down a legend about some heroes fighting a lich. When the lich's castle exploded, in the resulting fight, a great sword was seen flying away from the castle. They tracked down greatsword through local rumors and legends. At the end of a 6 hour quest they found it in the hands of biclops King. The biclops knew it was magical but it never worked for him and was more of a symbol of office. So after taking on a ash giant by herself she got the sword. Now what kind of weapon should I give her? I thought about a bastards sting but that is way too powerfully. But I don't know what kind of weapon to give. I mean the party devoted almost an entire day tracking down this weapon I just can't seem to think of something that would work. It doesn't help that it is midnight and we literally just finished the quest line about 20 mins ago. Any tips or advice?

[UlagSonofNone]

Unholy Avenger. It would make sense for it not working for the Biclops and all you have to do is change it from a longsword to a greatsword or bastard sword. It is a fairly powerful weapon, but you can just weaken it a bit until the sword decides she's powerful enough, like give her it's benefits in stages. At start it's a plus 1 cold iron, then plus two then plus 2 unhily finally getting to be plus 3 unholy.