In Sagrada Reset, one of the main characters possesses the ability to reset the world to a point in the last three days she has 'saved' at, which includes resetting her own memories.
Until she meets Kei, nothing changes after the reset as she is unable to know it ever happened. Yet she does understand how her power works despite never being able to witness it and she has been using it unsuccessfully for years.
At first, I thought everyone with an ability would just know what their ability is due to the setting, but in later episodes we hear of an incident where someone was injured using their ability for the first time, not knowing what it was, which suggests this is not the case.
So how did Haruki know what her power was before meeting Kei?