忘却の旋律 (Boukyaku no Senritsu, The Melody of Oblivion)
A media-mix project by GJK, an initialism of GAINAX, J.C.STAFF and Kadokawa shoten.
Its manga version, written & illustrated by Katakura Shinji, and 2004 anime series, by J.C.STAFF, are almost entirely unrelated to each other.