紅一葉 (Akahitoha)

紅一葉 (Akahitoha / A Single Red Leaf) is a song composed by Kurousa-P and originally sung by Hatsune Miku; which only reached 300,000 views. Megurine Luka's version was uploaded a year later; and reached 1 million views.

Aside from Cantarella and Senbonzakura; it's one of Kurousa-P's most notable work, in Nico Hall of Fame (exceeding 1 million views)

Note that this page covers more to Luka's version than Hatsune Miku's.
 * Nicovideo broadcast
 * Youtube broadcast (with subtitles)

Background
The original song sung by Hatsune Miku was uploaded on February 29th, 2008. It was well received with over 300,000 views, however, Luka's version uploaded a year after the original on May 26th 2009, six days after it was uploaded; reached 1 million views on June 1st 2009.

Luka's costume was featured in the online game TinierMe, and also featured in a few albums such as EXIT TUNES PRESENTS VOCALOVERS and EXIT TUNES PRESENTS VOCALODREAM. KarenT licenced Akahitoha's singles and is available for purchase in iTunes store.

The song basically tells of a woman who "never miss the water until it's gone". She realized the happiness and love for the man right after he was out to war. In the end, she watched the man out to war and promised to love him for eternity.