These are Friday Fiesta and Sunday Siesta! Two twins that are very much the opposite of each other, yet unseparable. Their dynamic is kinda like Maud and Pinkie.
Friday is a really (maybe a bit too much) energetic and fiery pony, and maybe slightly (read as really) annoying sometimes who can’t seem to tell “thrilling excitement” and “life threatening danger” apart. He’s a big party pony and usually has the craziest ideas that might end up with things catching on fire (“oh but doesn’t the adrenaline and the danger feel so thrilling?”). He’s very very energetic and can’t seem to sit still or focus in one single thing for long, and truly has a talent for making things blow up and catch on fire.
Fortunately, Sunday is there to put out his messes, she’s often seen dragging rainclouds around to put out the fire and explosions. Sun is a very quiet, sleepy and tired, and she kinda looks dead inside sometimes. She sleeps almost all the time, if she’s not dealing with her brother’s messes. Friday always tries to drag Sun in whathever he’s planning, even if it means pulling her by the tail.