Yuzuru Otonashi is a bit of a loser. He's dropped out of school and is working a part-time job which earns him just enough money to eat.
The only thing that really gives him reason to get out of bed in the morning is visiting his sister, who is hospitalized with an illness.
For Christmas, he sneaks her out of the hospital to take her downtown to see all the trees lit up and buy her a present.
It's not clear if she dies because of this, or merely shortly after.
Otonashi decides to dedicate his life to helping others. He returns to school.