Ok heres my attempt at Red Fel (i may return later to improve this)
Red Fury was wielded by the legendary bard Red Fel. It was said that Red Fel was so Evil, so Convincing, and so much Fun to be around that Orcus gave him a permanent invite to hang out in the Abyss and that Asmodeous once loaned him the Ruby Rod. Alas, all Evil things must end and Red Fel met his. No one knows how he died, but many Binders know that he is now a Vestige, but his followers are sure he could leave if he just asked the universe nicely.
Red Fury is a unique +1 Cursespewing Harmonizing Enervating Greater Dislocator Keen Rapier, that, when wielded by someone with an Evil Alignment, activates a permanent magic circle against good, centered on Red Fury. This can be suppressed as a free action (mental). If wielded by a person of Good Alignment, Red Fury automatically hits them for a critical hit the first time they roll to attack with it. It will do so again 1d4 rounds later if they continue to wield Red Fury. If a person of Neutral Alignment wields Red Fury it is just a +1 Cursespewing Harmonizing Enervating Greater Dislocator Keen Rapier.
Spoiler: The logic behind this (if you can call it that)I see Red Fel as an Evil Bard, who would much prefer to Diplomance you to his side instead of beat you into it. However i know he is terrifying when crossed (just look at some of his suggestions when he's in a good mood ) so a weapon based on him should be just a horrifying. Also, favoring his subtle side, this weapon works well for those who use it tactically. Smack the goody goody and poof him out of your circle, now hes stuck out there.