Kamen Rider 555: Grotesque Flowers

Kamen Rider 555: Grotesque Flowers is a novel written by Toshiki Inoue in 2004.

Controversy
The novel featured a controversial and disturbing scene where a revived Masato Kusaka violently raped Mari. This did not sit well with fans and there is much debate as to whether or not this novel should even be part of expanded universe canon because of it. However the Kamen Rider 555 novel that came out in 2012 considers those events canon to the overall story. Some fans now consider both novels to be non-canon as the uncomfortable subject of rape is something that has never appeared in the franchise before or since.