Anohana: The Flower We Saw That Day: Season 1 (2011)

Five childhood friends grow apart after the death of Meiko Honma, close playmate of them all. Jinta Yadomi, leader of the group when they were kids, neglects high school and lives as a shut-in when he unexpectedly starts seeing the ghost of Meiko, who can only interact with him and no one else. She has returned to ask Jinta to fulfill the forgotten wish she made as a kid.