AMNESIA

This story takes place in a fictional town, in a fictional country, in a fictional world. One morning, a young lady awakens to find that she has lost all her memories prior to that morning. Her life, her relationships, her very name—all gone. All that's left is a cell phone with numbers and names she doesn't recognize and Orion, a young boy that only she appears to be able to see. With Orion's guidance, she struggles to make sense of herself, a boyfriend she doesn't know and the thousand and one little things that make up a daily life. But with no memories left, the only alternative is to forge new ones, even if that means leaving old loves behind. (Source: Sentai Filmworks) — Description from AniList community (anilist.co).