I honestly have never [interacted with] a human person and gone "Wow, she's just like a cat." Or "He reminds me of a puppy!" But I see this all the time in manga. Maybe all these manga characters have more imagination than me...
Why does your own statement have editorial brackets?
"Some things are better left unsaid. Some strings are better left undone. Oh, believe, some hearts are better left unbroken. Some lives are better left untouched."
As a writer myself, I brainstormed just now and came up with about 10+ other ways their childhood friendship could’ve been introduced that would’ve actually helped the pair synthesize more, as opposed to just giving us poorly written randomness