Jinrui wa Suitai Shimashita: Nonbirishita 4-koma

A long period of low birth rates has led to humans losing territory to other species that have filled the resulting ecological gaps. Faeries, small intelligent creatures just ten inches tall, now dominate Earth while only a few humans remain. A young girl named Watashi decides to return to her hometown to take over her grandfather's role as mediator between humans and faeries. She soon discovers the position is more complex than anticipated, requiring wisdom beyond her age to fulfill her crucial task.