Da Capo I season 1-2
Junichi Asakura lives with his adoptive sister Nemu in the crescent-shaped island of Hatsune Jima, a place where cherry blossoms bloom throughout the year. In this island, people have mysterious powers and attributes. For example, Junichi has the power to see other people's dreams, and he was also taught by his grandmother to magically create sweets. One day, Junichi's cousin and childhood friend, Sakura Yoshino came back from America all of a sudden. To Junichi's surprise, she looks exactly the same as the girl that moved away six years ago, and hasn't aged one bit. And she came back to remind Junichi of their childhood promise... It is a bittersweet tale of magic, love, hidden desires, and unattainable dreams.

Da Capo II
The protagonist, Yoshiyuki Sakurai, was born when Sakura Yoshino, weary of being alone for so long, wished upon a prototype artificial wish-granting magical sakura tree for a family. Similar to its predecessor, the story takes place on the same island, Hatsunejima, in Japan, and set fifty-three years after the original anime. The Asakura sisters are the granddaughters of Junichi Asakura and Nemu Asakura from the first Da Capo. Sakura Yoshino and Junichi are the only returning characters, and Nemu is the only other character to be mentioned by name. (Taken from ANN)

Affiliated Groups

http://www.crunchyroll.com/group/Nanoha_Omake