I'm guessing someone doesn't like being called short... especially since that was three years ago. Or grade 3.
Don't say such rude things...Eh.... Nacchan?
Nano?It's not break time anymore, you know...Millimetres!?Saying millimetres, you...She's about this tall!You haven't even changed a single bit...7 Years-worth of growthYou don't remember!?That's right!On the other hand, are you really Tsuttsun?That's when I was in 3rd grade!!Pi!I've gotten bigger by two millimetres!♪Hold your horses! There's no way that Nacchan would be that big, is there?It's me!
Nanakusa Nazuna!!She uses 'boku', the boyish pronoun