K-on!!, but the rampant tea times makes everyone a unhealthy shell of their former selves... (besides Yui and her stupid metabolism keeping her thin >3<~)
I'm so braindead and horny and brain fried right now I cannot write proper descriptions so I'll respect your ask by listing my headcanons for obese Ho-kage girls:
Ritsu, while blobby all over just like the rest, has most of her gains in her hips and legs and enormous ass. This renders her somewhat-mobile compared to the rest of the crew, yet she has the most trouble squeezing through doors;
Mugi is a bona-fide ball of lard. Round, filled-out in an almost spherical fat distribution pattern. She is also the horniest of them: the rest treats their condition as an inconvenience. Mugi though? She's leaned into it fully. Reading fat fics daily, looking red in face and flustered;
Mio: somehow all the fat made her grow a little taller to the point she towers above the rest of the girls for a head or two. Most of her fat went to her boobs, which sag to below her waist and slosh constantly, growing bigger every day.
Yui, as you rightfully mentioned, is the sole exception. Somehow she is the only one of them all to LOSE some weight! She's a little pudgy, despite eating for ten of them combined. You guys wanna go jog or something? I'm so full of energy..! She exclaims after their routine cake stuffing session, while the rest of the band is lethargic and fighting the inbound food comas;
While not strictly a member of the club, Hirasawa Ui, is the polar opposite of her sister. She's immense and had grown immensely lazy, to the point they had to arrange a deal so she could get home-schooled, since she's grown too lazy to get off her bed anymore. Yui wheels her carts full of breakfast, lunch, dinner, as well as night snacks at the same time.
Yui dashes to the door to the closet that seems to store whatever is making that weird sound. It sounds like... a mix of creaking, groaning, munching...
Yui... ggullpp... no, don't open--! Tsumugi tries to prevent the disaster from happening, but the ball of energy of the elder Hirasawa is an unstoppable force. The fluffy hand of the genki turns the doorknob, and the force shoves her aside. The door swings open with immense force, and a pile of some pale substance pools out, filling half of the room.
H-huh? Wh-what's wrong?! Why's it feels so breezy all of a sudden? Azusa's voice, deeper and huskier, yet remarkably hers, rings from the center of the pile in the closet, she pushes a HALT button and the conveyor belt that has been supplying her with a never-ending stream of cakes pauses. She wipes some icing off her blobby face and cranes her head to face the intruders. Excuse you, can I have some privacy!?
Yui lays propped by the wall, passed out from hitting her head from the impact of the pressure of the packed fat.
S-sorry Azusa-chan... We forgot to tell Yui about your new hobby...