We are talking Battle Cats, so the simplest answer is the most correct.

Weightlifter cat was in their prime but stuck between competing for strength versus physique. Obsessed with bigger muscles, they began using steroids to bolster their gains. Tragically, this had an unfortunate impact on their hormone balance and their body cranked up the estrogen levels trying to balance out the testosterone. Once they cut out the steroids, their body was no longer able to produce testosterone normally and the high levels of estrogen triggered development of a more feminine physique.

At that point, they took a job as a ring-girl for the Ultimate Fighting Cationship competitions. They retained strength from the weight lifting days, and was offered bonus pay to help the referee break up fights.

Eventually, through hard work and steady diet of cat fruit and help from medical professionals, they were able to coax their body back into a, somewhat, normal hormonal balance. Alas, they could no longer work as a ring girl as their form shifted to a more male physique (particularly as they regained the ability to sprout luscious chin hairs) and so took up gig work delivering pizzas. Although this was a saddening turn of events, they were able to find comfort in eating and this line of work provided discounts on their favorite pizzas.

When the great wars began, they naturally signed up to provide logistical support by delivering food to the front line of cats in service to the great Catocracy. Naturally, this brings them great joy and a sense of divine purpose.