The story takes place in a quasi-medieval period. It tells of twins who were separated shortly after they were born. The reason behind was that one of them (Rin), was chosen to be the next Diva, and her destiny is to sing for eternity to keep an ancient Dragon in its slumber.
After Rin's brother (Len) was old enough, he began searching for his sister, to free her from her fate of being a Diva.
Note: This song is known as "I Look for You in the Sky" in western fandom, but "The Sky Where I Look for You" is more suitable. This tradition comes from Motokokusanagi's mistranslated title.
In the beginning of the video, Miku was shown in a cave, followed by Teto (the previous Diva), who was killed by the dragon. Then, Rin was taken away from Len when they were babies, and years afterwards, Len started his journey in search for his twin sister Rin who was chosen to be a Diva; a singer who sings to a dragon so that it may bless the country.
Yet the only way for a Diva to escape her role is to either be killed by the dragon or for another Diva to replace her.
Along the way, the other characters (Vocaloid) could be seen too.
~Synchronicity~ 光と影の楽園 / ~Synchronicity~ Hikari to Kage no Rakuen (Paradise of Light and Shadow)
This is the second part of the Synchronicity series. In this part, Len infiltrates the castle of Luka, a pythoness of the empire, to find Rin. There Meiko, who was nobly born and became a fencer of the empire, attacks Len. However, during her fight with Len, he reminded her of her old friend Teto, who sacrificed herself for Meiko by becoming a Diva. Thus, Meiko joins him on his journey to save his sister.
Len, Meiko, Gackpo and Kaito join together to travel to the dragon's lair and confront Miku, the Dragon's guardian, who was blinded and forced to wear a magical mask by the clergy. However, Len defeats her by destroying this mask.
The ending of the PV shows Len jumping off a ledge towards the distant figure of Rin, hand reaching for her, with tears of joy in his eyes, leaving us with a literal cliff hanger.
Note: This song is known as Requiem of the Endless World in western fandom, but Requiem of the Self-repeating World is more suitable. This tradition comes from Motokokusanagi's mistranslated title.
The third installment is included in Hitoshizuku-P x Yama's first major debut album "EndlessroLL".
The song ends the three year long cliff hanger of the series, with Rin and Len finally reunited. Their wishes completely opposite to each other, they faced their fate. The ending and conclusion of the series may be interpreted differently by different viewers.
It was once claimed that "The series was cancelled in May of 2010" and "There will be no third installment". An incomplete video of the third installment was put up on the Nicovideo broadcast, but was soon taken down. Afterwards, this rumor was denied by Hitoshizuku and it was confirmed that a third installement was in works. The third part has now been released on Niconico, and on YouTube.