Answer:
My first is in wield, sever bones and marrow. My second is in blade, forged in cold steel. My third is an arbalest, and also in arrows. My fourth is in power, plunged through a shield. My fifth is in honor, and also in vows. My last will put an end to it all.
There are millions of me. I am very small but when moving fast I am deadly.
Different lights do make me strange, thus into different sizes I will change.
A kind of weather that comes your way, but add a "D" and it will run away
Turn us on our backs and open up our stomachs you will be the wisest of men though at start a lummox.
Almost everyone needs it, asks for it, gives it. But almost nobody takes it.