Last week, we showcased a few anime celebrations of the summer festival Tanabata, when lover deities Orihime and Hikoboshi (associated with stars Vega and Altair respectively) can cross the Milky Way to be together. Producer Manbo-Dead-Behind-The-House-P has a new Tanabata trilogy of music videos with avatar-less Vocaloids VY1 and VY2 as Orihime and Hikoboshi and Gumi singing the third, Kappa part.
From translator vgperson's comments
Japanese folklore lesson! Tanabata is July 7th, and it celebrates the legend of Orihime and Hikoboshi (associated with stars Vega and Altair respectively), two deities that were separated by an entire galaxy for being too lovey-dovey to do their jobs. Got it? Good.
Additionally, the Milky Way (Amanogawa) is more or less considered a literal river for whatever reason. Also, youkai are mythical Japanese monsters, but I think you could guess that one.
Manbo claims the songs can be watched in any order, but it seems pretty clear to me that there's still a "proper" one, which is how I uploaded them. (Incidentally, I first watched them in the exact opposite order.)