@GoggledAnon
I haven't seen the raws, so take this with a grain of salt, since I don't know if it used any specific pronouns.
Since the sword said that it was made as a concept of piercing, I think it's the good ol' case of a conceptual representation.
That said, since it has been nurtured by Kobayashi's experiences, I think it safe to assume that sword-chan is a girl and the Mr. is just an interpretation.