Freshwater by Akwaeke Emezi

Ada has always been unusual. Her parents prayed her into existence, but something must have gone awry.

Their troubled child begins to develop separate selves and is prone to fits of anger and grief. When Ada grows up and heads to college in America, a traumatic event crystallises the selves into something more powerful.

As Ada fades into the background of her own mind, these 'alters' - now protective, now hedonistic - take control, shifting her life in a dangerous direction.