Beyond the Russells, the main cast included: , a teacher who discovers her late father’s hidden double life; Ren Watabe as Kentaro Randa , Cate’s long-lost half-brother; Kiersey Clemons as May Olowe-Hewitt , an entomologist caught in the mystery; Mari Yamamoto as Keiko Miura , a 1950s scientist who bonds with Lee Shaw and Bill Randa; and Anders Holm as Bill Randa , a key founding member of Monarch. Recurring cast members included Joe Tippett, Elisa Lasowski, John Goodman, and Tamlyn Tomita.