It's The Splatfest with the theme being Fat Vs. Inflation, Pearl had fattened up a ton getting a huge fat body, and Marina getting an inflated body

Pearl: The people have spoken! They'd rather worship this flabby princess than your balloony butt!

Marina: I must admit defeat. Honestly, being this big is kinda weird

Pearl: Oh you know you like it Marina, plus I love this feeling of being this big!

Marina: Ok you got me Pearlie I did enjoy it, plus I think you look cute being that big