The main benefit of Kerah's sword is to give everyone "Guardian Angel" (a perma-Vine of Life spell when invoked) rather than to use.
All right, that did it. I'm out to find a BloodSlinger sword this time!
The Murakata blade, though, I didn't think could be blessed. The Tomomari Katana I thought was much better because you can bless it WAAY up.
BTW, quite often, the undead blacksmith in Castle Shurugeon will drop a Nightblade, which is a pretty danged good sword for that early in the game. If he doesn't, try reloading and fighting him again to see if you can get it. It blesses up very well as well.
-Sazerac