In a certain high school on the westcoast, two teenagers named Jim and Rick discovered a computer program that could rewrite reality itself. After Jim used the program to transform Robin Foster (a girl who had just publicly embarrassed him) into an anthropomorphic catgirl with six large breasts, then after liking the result he decided to spread the change to the female half of the human race, with one caveat…only Robin Foster would be aware of the change. Sure enough, every female on the planet was an anthropomorphic catgirl with six sizable breasts (depending on their age of course), equally used to walking on two legs or all fours with the only forms of clothing being collars and skirts (or other clothes bellow the waist if there was a need). Unfortunately, Jim had neglected to remember his friend’s cat allergy and his attempt to fix it turned Rick into a catgirl as well, this followed by his decision to choose a different animal resulting in all catgirls turning into doggirls of every conceivable breed, as well as skewing the gender balance to 3/4 female and 1/4 male. What follows is his friend Rick ending up as a labrador girl while his original girlfriend Sharon is a collie and Robin is an irish setter and the four of them are now in a relationship with only Jim and Robin aware of the old reality and only Jim able to do anything about it due to password protecting the program. However unbeknownst to Jim, the command of “only Robin Foster would be aware of the change” applied to all with that name, a name that was Gender Neutral.
To this end it is the suggestion that each chapter would be a vignette exploring various people named Robin Foster as they notice this change around them, a change that others are unaware of treating the altered world as normal. You could have a husband noticing the change on his way home after dropping his kids off only to watch the world change around him twice then arriving home to find that his next-door neighbors were now both female and married to him as well. Another possibility would be a young executive who recognizes the changes in the middle of a meeting with more women in the room than earlier and navigating the way this change effected corporate culture and the workplace. I Europe a young man and his girlfriend are in the middle of an afternoon make out session when the world shifts and the man finds himself now a woman as a hetero moment turns first catgirl yuri and then doggirl yuri, followed by the original lady of the pair suggesting at the end that they go looking for a guy later tonight to share.
Main characters other than the original duo (and their victim) who would be 18, the rest of the intended characters should be in the early 20s to mid 30s. My final scenario suggestion would be the early morning of a trans man who is clinically depressed with being unable to afford what they need to transition when the change hits and how they react to it and seeing how it changes their outlook on life.
The catgirls and doggirls would be fully anthropomorphic, with the doggirls having more of a variety of sizes equating to that of normal dog breeds, and in both cases the women would have six breasts in the average to large size range. Women in both altered realities usually wear nothing from the waist up and shoes usually being unnecessary.