In an alternate timeline, humanity was driven to extinction by their own selfishness and stupidity, leaving only animals to inherit the dying planet. Animals eventually evolved to have more human-like traits, such as walking on two legs, developing thumbs, as well as critical thought and speech, until Felis was founded 500 years later, with Cassian being born as crown prince 500 years later. After a portal brings the user (a human) to this timeline, they work with Cassian to find their way home.