Koyomi is Jun&#039;ichi&#039;s homeroom teacher, one of the faculty&#039;s science teachers, and Kotori&#039;s older sister. She is also a researcher at the Amakase Laboratory, and in charge of the Miharu android. In the Second Season, she is a new mother, and her strict composure rapidly crumbles when she talks about her baby.

Every year the flowers bloom. Mysterious Cherry Blossoms blooming all over a crescent shaped island. That island is the island of Hatsune... 
The main character who goes to Kazami Academy, Asakura Junnichi, has the power to see the dreams of other people in his sleep. He was also taught magic by an old lady that allows him to create sweets. 
One day, Junnichi seems to have seen someone's dream again while he was sleeping. Inside that dream, a girl who was a childhood friend of his appeared. But, he was woken up by his sister Asakura Nemu, forcing him to come back to his regular life. Nemu doesn't actually have any blood relation to Junnichi but their bond is deeper than other real brothers and sisters. So deep that it gives the illusion that they're lovers. 
It was another peaceful normal day waking up early in the morning and going to Kazami Academy. Together with childhood friend Amakase Miharu, the academy idol Shirakawa Kotori, the two sisters Mizukoshi Moe and Mako who prefer eating nabe on the school roof for lunch. Going through their day as usual, their childhood friend, Yoshino Sakura, who they thought had moved to America suddenly appears. It was a surprise for Junnichi and Nemu. Sakura tells them, "I came to finish the promise we made during our childhood"... 
(Source: AnimeNfo and AniDB)

Hatsune-Jima was once well-known for its cherry trees, which would bloom no matter what time of year it was. Two years ago, the island's cherry trees lost this ability and all became ordinary cherry trees that bloom only in the spring. Jun'ichi Asakura is now a graduating senior at Kazami Academy, and is surrounded by many close friends, old and new alike. On a stormy summer day, a mysterious young girl, Aisia, arrives at Jun'ichi's door. She is looking for Sakura's grandmother to study magic, ultimately hoping to bring happiness to everyone. When she discovers that grandmother Yoshino had long since passed away, she joyfully assumes (thanks to his error in judgment) that Jun'ichi is able to teach her. Even though she finally understands that the only magic he's capable of is conjuring Japanese confections, Aisia continues her search for magic on Hatsune-Jima. Amid the chaos of her search, Kazami Academy hires new medical staff.
 
(Source: Anime News Network)

This two episode OVA retelling of the first Da Capo series with the "what if" Asakura Jun'ichi were to return Shirakawa Kotori's feelings.

Koyomi Shirakawa