(from ebookjapan):

Hideko Mizuno, the mistress of Shojo Manga, depicts the tragic love between Robert and the mysterious girl, Cecilia, in this fantastic love romance.

Robert, an unsuccessful young painter, meets a young girl, Cecilia, playing in a foggy park. Robert is impressed by Cecilia, who confesses to Robert that she likes him and leaves him. Robert paints a portrait of Cecilia, which leads to the sale of his paintings and Robert finding success.

A week later, Robert meets Cecilia again and is astonished to see a very grown-up Cecilia...!

Manga adaptation of A Portrait of Jennie.