What is the best weapon in fire emblem radiant dawn?

Lubu's Demon Bane.

That's not nessicarily the best weapon, depending on who you like to use or what level you are doing. Like at the Battle of Hua Lao Gate, Lu Bu and his weapon might be a good idea. But maybe you're awesome like me and like to use Zhou Yu's Elder SWord to beat Lu Bu (I did it with him, too).