16+12: Nijuuhachi

Yuu Komakida died in an accident on her 17th birthday, but she's been reborn as Shiyu Koburagi with the memories of her prior life intact. Now 12 years old, Shiyu has been reunited with Chiharu, who was so fond of her pre-reincarnation that he proposed to her. He was 5 then, now 17. Chiharu's heart has been filled with grief because of Yuu's death, but...

(Source: Shogakukan, translated)