MFW

I looked it up and Sweet Mask does indeed only care about A-rank and above. Fubuki's got a bit of an inferiority complex to her sister, so i think she tries really hard to be the best. I'm guessing she puts a lot of value on being #1

I can't really blame her, she has, for her entire life, played second fiddle to her sister, one of the strongest heroes that the world has ever known (As far as we have seen, of course)

The only thing she has over her is her height but she took that shit to heart and it is only now that Saitama showed up that she is beginning to improve her world view by seeing someone so effortlessly be better than basically everyone, but doesn't let that go to their head like her sister

And he flat out saved her life, so there is that (I would like to point out that the explosion happened behind her, and Saitama was in front of her, though granted this picture doesn't show that)