I have something of a set of characters or setting but I haven't been able to think of exactly what story should be told with them. It involves a world where there are breeds of girls who appear human but with additional animal features like ears and tails (basically neko girls and such).

It could be a sci-fi setting in which they were created with gene splicing and are raised on a special planet or it could be an anime alternate reality where all girls are animal girls of some sort and that's just the way it is.

I've listed the species I had in mind along with their attributes. Their growth rate is faster and life span shorter since they are meant as snuff toys but I've included what ages they tend to look like physically.

The story could be presented as a tour on the pet girl planet (sci-fi) with a guide explaining the various girl species the traveler can play with. Or it could be a more anime inspired slice of life story, with short fluffy vignettes about the main character doing things with each type of girl that they maybe encounter during their day (or vignettes of multiple characters who each own different 'pets').

Puppy Girls (9-14)

They look just like human girls only they've got floppy ears and a furry tail that wags. These ones love to give you attention whether its cuddles or kisses and they're extremely loyal. They'll be scared of the more extreme things you plan to do to their innocent bodies but they won't disobey even if they have to nod and whimper as you wrap your hands around their throat and state that it's time for you to put them to sleep.

Cat Girls (9-14)

With their fluffy pointed ears and twitchy tails they're just as cute as puppy girls but they couldn't be more different in personality. They're well known for their brattiness and they'll fight back against your advances although it's clear that they enjoy having their pussies played with even if they're too stubborn to admit it. One thing they're not shy about enjoying is the chance to help to make other girls suffer and die for fun.

Bunny Girls (10-13)

Bunny Girls are energetic and slender beauties that often grow A or B cup breasts early to compliment their big pointy rabbit ears. There's only one thing on their mind at all times and that's sex. They're so eager for it that they'll agree to anything in exchange for being fucked. Even if it means they'll experience pain, mutilation or certain death they'll enthusiastically go along with everything just to get to that one orgasm you promised them.

Mouse Girls (8-11)

Mouse Girls are petite with several unique colors of pixie hair although most are a very white shade of blonde. They have very short life spans but make up for it with their rapid breeding. Knowing few words they have a limit understanding of the world which contributes to their poor sense of self preservation. Most commonly they're gathered and killed en masse, each one snuffed out for only a second or two of entertainment a piece.

Horse Girls (10-16)

Horse Girls have firm athletic bodies with long gorgeous legs and skin ranging from pale to the darkest midnight. They're stronger and hardier than others and are obedient enough to accept being roped or retrained. While their pain threshold is average they're capable of screaming their way through enormous amounts of punishment and blood loss before it actually kills them, making them perfect for drawn out torture and horrific body modifications.

Cow Girls (12-18)

Cow Girls are easily recognized by their big bouncy breasts as well as their equally juicy thighs and buttocks. They're very cheerful and love to have their boobs played with and squeezed and you can even milk them. Of course they're aware that they'll eventually be food and so they'll happily line up for slaughter secure in the knowledge that you'll enjoy eating them just as much as you enjoyed playing with them.

Maybe there are some other pet girls who could be described as well?