The soundless voice, proof of life, and endless wedge series tells a story about a girl (Rin) who knew that she was about to die, and a boy (Len) who takes care of her. In the end, Rin died because of her sickness, before Len could even say that he loved her. Years later, Len remembers their time together and still kept Rin deep in his heart.
Len sings of how he cannot live without Rin and how they are supposed to share the same soul. He wants to know if she is lonely or in pain so that he can comfort her, for he's aware that she is withering away.
Len states that he was in love with Rin, but was to late say it and wishes for his voice to be taken away and to be given it to the one he loves. In the end he wishes to die with her as his voice is now soundless without her.
Rin knows that she is dying but she wishes to keep singing, as she wants something to remain as proof that she existed. She expresses her pain and loneliness around her, and how the one thing she doesn't want to disappear is Len's smile.
Rin continues to exclaim that she and Len are connected and that she will always be with him. She is also aware that Len is in love with her and it is implied that she loved him back, as she wanted to thank him for everything.
Endless Wedge happens years after Rin died. Len remembered the days he spent with Rin, he wanted to hold her again, and remembered the times they spent together. How Len gave her happiness, and how Rin gave her smiles for him, and was sad they couldn't have a future together.
In lonely nights, Len remembered Rin's singing voice, helplessly crying. He sang Rin's song, 'I do not want to sing a sad song' (the lyrics from Proof of Life). Len remembered Rin's voice, it was still there, and in the end he said, forever he will always love Rin.