So I'm gonna cheat a little over here since Mirai's weapon is technically her ability. And she can actually conjure her blood into anything she wants, but I'm going to stick with her sword.
Although it is faulty against youmu lineage, I still think it is a badass weapon. You don't need to carry anything around with you (except for your blood of course xD). Isn't that convenient??
Even tripping looks badass (; @VinMcCarthy