Heh, both cute arguments the characters have about their roles as well as cute close-ups in that last one.
Why is the image of someone leaning against a giant's nose like that so adorable?
I think, because it shows, beyond a doubt, that they're not afraid of their giant friend.
The nose/muzzle is right above those big sharp teeth, you don't even put your hand near a strange dog's head for fear it might bight you right? So we inherently know the muzzle can be a dangerous place, you might be bitten, or worse if you're actually facing a giant. But the fact that she feels comfortable leaning against Kali's nose so casually shows a complete lack of fear, and a trust that Kali simply wouldn't do anything like that to her. She might joke about it and flash her fangs for fun, but ultimately Jerry knows she's safe.
And Yes Narzain these girls use the fourth wall for target practice, they care not for its presence.
But Jerry does have experience countering Kali's teases and vice versa. Being childhood friends they have a healthy bit of playful competition behind them and are no strangers to each others jokes.