Tenshi Tokei

Tenshi Tokei summary:

Mikami Tsubasa has been away from school due to a heart condition. On Christmas Eve he decides it's time to start a new life and runs away from home! But before he can get far his childhood friend, Gin, gets into a serious accident. Tsubasa, in desperation, pleas for someone to help his friend. His call is answered by someone rather unexpected though, someone calling himself an "angel"...