I like how the secret weapon ... failed.
And I like even more that Hana was like, eff that, let's try it again! And that time, Nana, who thought Hana was too whipped, actually fell into it.
You can't say the auithor didn't put some thought into making the hamster's holding her own plausible. She had the Rocky-like training montage, she had the planning sessions, and also - Nina is not that big - she doesn't outweigh Hana by very much, she's taller but equally slender. Against a real bruiser girl a lot of Hana's stuff wouldn't work as well. Who'd have thought an author could get us to root for a cute, tiny, cuddly little hamster of a girl to go get the crap beat out of her?