The Whale Imagin is an Imagin and antagonist in episodes 15 and 16 of Kamen Rider Den-O.
Kamen Rider Den-O
The Whale Imagin took a man who wished to get rid of his drinking problem as his host. In his attempt to complete the wish, Whale Imagin opted to attack anyone who knew about the drinking problem.
The Whale Imagin later travels to the past and attacks people who were having a hanami party under a starlit night sky until he is confronted by Den-O Sword Form and Gun Form. He is destroyed by Den-O Sword Form.
The Whale Imagin later appeared among the massive army of Imagin commanded by the Death Imagin that invaded both the past and the present as part of Kai's plan to ensure the Imagin's future.
Kamen Rider Decade
A Whale Imagin appeared as one of several Imagin that attempted to get Natsumi Hikari to tell them her wish while she was trapped in shifting dimensions during the destruction of the worlds.