Time travel is not exclusive to the protagonist.
It can also be a supporting role, or even a secondary role.
The identity before time travel can be various, such as a doctor, a special soldier, an agent, a magic chef, a certain expert...
They each used their strengths to change the world.
Cake, French fries, hamburger; Gender equality in high school and college entrance examination;
Quadratic inequality of one variable; glass toothbrush Internet.
And...
Fan-original romance comics; Danmei Prey cross-dresser;
Xipi dismantles the opposite camp; Tsundere is in the second year of magic.
The princess who is a middle school student and stays at home;
The sickly and crazy female official;
The European Emperor's narrow-eyed female general;
The sister-controlled emperor;
Writers who only dig but don't fill;