Its unknown when or how Strawberry got Custard but this little kitty is her best friend, maybe even more-so then the others. Custard makes many more appearences then Pupcake but sometimes only Pupcake will appear.
Custard is like any other kitty, she's very friendly, kind, gentle, easy to please, and berry playful! When someone seems upset or in a bad mood, Custard will come by to try and perk them up. She is rarely ever upset or tempermental, and not at all picky about the things she is given. She likes to try and help the best she can. Since she is like most cats, Custard happens to be very playful. Trying to play with Strawberry's scroll paper she used for drawing, her pencils and pens. Custard also rubs against things or people she likes, such as in one episode when she rubbed against Berrykin Bloom while he was in the middle of talking.
Most likely when Pupcake goes with Strawberry, Custard stays back to nap or play with something or someone else.