Tomoya Okazaki is a third year high school student resentful of his life. His mother passed away from a car accident when he was younger, causing his father to resort to alcohol and gambling. This results in fights between the two until Tomoya's shoulder is injured in a fight. Since then, Tomoya has had distant relationships with his father, causing him to become a delinquent over time. While on a walk to school, he meets a strange girl named Nagisa Furukawa who is a year older, but is repeating due to illness. Due to this, she is often alone as most of her friends have moved on. The two begin hanging out and slowly, as time goes by, Tomoya finds his life shifting in a new direction.
-Anime News Network

Kanon's story revolves around a group of five girls whose lives are connected to the same boy. Yuichi Aizawa is a second-year high school student who had visited the city where the story takes place seven years prior to Kanon's beginning. The story opens on Wednesday January 6, 1999 when Yuichi arrives in the city and is very detached from it and its inhabitants. Prior to his return, it is decided that he is to stay with his first cousin, Nayuki Minase, and her mother, Akiko. After his long absence, Yuichi has forgotten almost everything except minor details of what happened seven years before and is in need of being reminded of what he left behind. Nayuki initially tries repeatedly to jog his memory, but is unsuccessful. Throughout the story, as he learns about the supernatural undertones of the city, Yuichi is reminded of the events of seven years ago.
-Wikipedia

This is an ordinary tale of the ordinary days spent in an ordinary town by an ordinary girl who learns that everything in this world is extraordinary ― or that nothing is. For in this world, there is a young man named Blackiris; a Mnemonicide par excellence. And there is a young girl named La; sweet and warm and gentle in all the ways that count. This is their story.
-Insani.org