I know that one, I will help you look for it.

First I found all the music in this delusional student union...

"DAYS", singer: FLOW, lyrics: KEIGO HAYASHI, KOHSHI ASAKAWA, composer: TAKESHI ASAKAWA, arranger: FLOW&Seiji Kameda (episodes 1-13) "Shōnen Heart", Vocalist: HOME MADE Family, Lyricist/Composer: KURO/MICRO/U-ICHI, Composer/Arranger: Takahiro Watanabe (episodes 14-26) "Sun "の真ん中へ(Taiyō no Mannaka e)", Singer: Bivattchee (ビバッチェ), Lyricist/Composer: Tsutsumi Shinichi, Arranger: Taiyō no Mannaka e) "sakura", Singer: NIRGILIS (ニルギリス), Lyricist: Aya Iwata, Composer: Minoru Kurihara/Ana Iwata/Takaki Ito, Arranger: Nirvana (episodes 40-49)

Ending theme "Himitsu Kichi (Secret Base)", sung : Takada Saoe, Lyricist/Composer: Takada Saoe, Arranger: TOMI YO (episodes 1-13, 26) "Fly Away", Vocalist: Izawa Mami, Lyricist/Composer: Izawa Mami, Arranger: Abe Jun (episodes 14- ( episodes 40-49)

Episode "STORYWRITER", by SUPERCAR "trance ruined", by NEWDEAL "draft any funk", by NEWDEAL "GET IT BY YOUR HANDS", by Watanabe Hiroshi a.k.a. Quadra "Niji" , by Denki Groove (episode 50) Time-lines, by Hiroyukl Kasal

Game version theme song "Realize", by FLOW (Eureka Seven TR1: New Wave, Eureka Seven: New Vision)