The new protagonist in Fire Emblem Warriors: Three Hopes is Shez.
Shez is a mercenary whose story begins after a defeat by Byleth, the protagonist of Fire Emblem: Three Houses. Surviving that encounter, Shez becomes determined to improve and eventually enrolls at the Officers Academy in Garreg Mach Monastery.
Like Byleth, Shez is a player avatar with selectable male and female versions. However, unlike Byleth, Shez has a defined personal identity, voiced dialogue, and a supernatural companion named Arval. Shez can join the Black Eagles, Blue Lions, or Golden Deer, creating three major routes: Scarlet Blaze, Azure Gleam, and Golden Wildfire.
A common mix-up is answering Byleth, since Byleth is central to Three Houses and remains an important character in Three Hopes. In the newer game, though, Byleth serves mainly as Shez's rival, while Shez is the playable lead. The game is also set in an alternate timeline rather than directly retelling Three Houses.