samurai katana help

I don't sell my weapons. I keep them. I went to the sage under the cave and found out I have 99% of all treasure, and I checked an anthology weapon list on the internet and found out I'm missing the chicken knife (I picked brave blade) and I'm missing a katana. The name of the katana on Anthology is called MonsterKiller. I checked some lists to see where to get it, but the only bestiary lists I can find are all japanese translation based. I compared the japanese and english weapon lists and I believe the MonsterKiller(Anthology) is the Murasame(FFVjap) and it says I can find the Murasame on a giant bird and on TwinTania. Well, TwinTania drops Tinkerbell, so that's out, and there is no giant bird on FFVantholgoy. I tried checking Zu's, but taht didn't work. Does ANYBODY know where to find MonsterKiller?
p.s. Murasame may not be the correct translation, but all the info looked the same. Please help!

Huge Birds drop Murasame. For some reason, they're called Big Butterflies in the Anthology translation. I forget where they can be found, though. Try the Island Shrine.

The Anthology translation plain sucks. Sorry.