The Rebeccas are the two twin girls in the leading Styx family, and the main antagonists in the Tunnels series. Their father is the Crawfly, and their grandfather is the Old Styx. The Rebeccas originally pretended to be Will's Topsoiler sister. The twins plan to release the Dominion virus and have the Styx reclaim Topsoil. They have been hunting down Will in revenge for trying to stop the Styx and killing their father.