東方アニメ歌クロスオーバー

Pretty sure there are a lot more, but I can only think of six currently. Coincidentally (well not really), they are all IOSYS covers.

Original: Cowboy Bebop - Tank

Cover: IOSYS - DEAD GIRLS BE-BOP!!

 

Original: Rozen Maiden - 禁じられた遊び (Kinjirareta Asobi)

 

 Cover: IOSYS - Fräulein Lilie (The Maiden Lily)

Original: Rozen Maiden - 聖少女領域 (Seishoujo Ryouiki)

Cover: IOSYS - 六十年罪業華地獄残酷歌 (Song for the Cruelty of the Hell of the 60 Year Flowers of Sin)

Original: Hidamari Sketch - スケッチスイッチ (Sketch Switch)

Cover: IOSYS - 恋色被害届 (Love-colored Damage Report)

Original: Tengan Toppa Gurren Lagann - 空色デイズ (Sorairo Days)

Cover: IOSYS: - 大空の高みへ ～The Legend of TANGO～(To the Heaven's Heights ~The Legend of TANGO~)

 

Original: Death Note - 絶望ビリー (Zetsubou Billy)

Cover: IOSYS - 絶叫クールマッチ (Screaming Cool Match)