Ao ni, Fureru.

Ruriko Aoyama, a second-year in high school, was born with a large, blue birthmark on her face. She has lived her life trying not to make a big deal of it, trying to avoid overly conscientious treatment by those around her. One day, Ruriko gets her hands on a notebook belonging to her new homeroom teacher, Kanda. He had written all of her classmates' names in the book, and next to their names: distinguishing physical features. However, Ruriko notices that the space next to her own name is inexplicably blank. When she confronts her homeroom teacher, Ruriko finds that Kanda lives with prosopagnosia – a disorder which prevents him from being able to make sense of and distinguish the human face...
(Source: MangaPlaza)
Note: Nominated for the Tsugimanga 2020 Award in the manga category.