So I'm new here and this may be a stupid idea for a post, but I'm gonna try it anyways. I am going crazy trying to find this sword even with the little hints I have so I figured if I shared my hints/ideas maybe someone else can figure it out and help me out. I'll start with the picture Hentaicrazed posted of it:
First of all, it is the third sword. To me that would indicate it cannot be found before you fine the iron sword but either can be found or has to be found before you are able to get the brood defender.
Second, I think it looks like Tiki when she transforms. It could be a tentacle or something, but Grope plants didn't look like that in Dusty's Castle if I remember correctly.
The description (which I know you can all read) says "never fails to please" which would support my previous thought.
Knowing all this I restarted the game and haven't figured anything out! I fucked everything as Eva, Alien Eva, and Bridgette. I went around and talked to everyone as Bridgette, when Tiki transforms for the first time with the vanguard I tried using Bridgette too, but no new sword. So maybe someone smarter or more clever (or just with a clearer mind) can figure it out and help me out! So if you get it please post a hint or PM me! Thanks
Also, I understand that because I know/deduced all this other people may have too, I'm just laying it all out in one place so it will hopefully help spark an idea in someone's head.