Yoko The Cherry Blossom

In 1940, Takaoka Masaaki works as a teacher in the agricultural division at a youth training institute. All of his students are drafted into the war which is nearing its end. He makes everyone promise that they will all meet again under the cherry blossoms upon their safe return. His students soon perish in the war.
Masaaki is wracked with guilt over their deaths. To comfort the spirits of his dead students, Masaaki attempts to develop a new species of cherry blossoms which can bloom under any environmental conditions from subtropical to Siberia cold weather (where his students died).
(Source: AsianWiki)