My favorite GRAVITATION song in the OVA is: "In The Moonlight"
This song is about Patiently waiting for the person you love to return to you after such a long time and to feel the pain of his/her loss.
Yuki wrote the Nittle Grasper song entitled: Shining Collection, and Shuichi was depressed that Yuki didn’t write a song for him, so he returned to his hometown, But he realized that he was happy that his idol (Ryuichi Sakuma) sang the song of his Beloved (Eiri Yuki) and decided to go back. As Nittle Graspre were performing “Shining Collection” on a Live World Wide music festival, Ryuichi asked Shuichi to come and sing with him, and after that, he called Hiroki and Fujisaki to come up on stage and they sang “In The Moonlight”, which they barely practiced, and out in the see of people watching the concert, he saw Yuki watching him sing.