Elizabeth the 3rd is such an elegant cat, It'd be a shame to leave her out of Mystic Messenger, otherwise known as Mysterious Messenger. Right now, even Saeran and V have routes, why not the cat that played a main part in developing 707 and Jumin's characters in the beginning and contributing a lot to the plot. Additionally, doesn't her fur just make you want to collect it and make it into a scarf?* Just look at her beautiful blue eyes, you're getting hypnotized to sign this petition, meow. 
*If you sign this petition, we guarantee a premium Elizabeth the 3rd c-fur scarf. (Not really though. No Elizabeth the 3rds were harmed in the making because we're not making any. Lol)