Sorry, this is not manga, but I'd like to mention The Idolmaster.
The original game of The Idolmaster is an arcade game about producing girls as idols.
However, the first anime series Idolmaster: Xenoglossia is a robot anime.
Girls ride big robots named "IDOL".
EDIT: Added some background of my understanding.
is one of first animation studios in Japan.
Mushi Production is known for Tetsuwan Atom which is the first Japanese anime series.
Mushi Production was founded by Osamu Tezuka who is "Godfather of Anime" and the Japanese equivalent to Walt Disney.
This studio was created by manga/anime creators (animators).
At Mushi Production, animator's opinion was most important and business-side people didn't have a voice.
Lacking business sense, Mushi Production bankrupted in 70's.
Sunrise is a spin-off company from Mushi Production.
The founders of Sunrise knew why Mushi Production failed, so they decided a new policy that have strong business executive members and animators can't poke to the business side.
For example, animators can't become board members of Sunrise.
At Sunrise, it moves in the opposite way: animator's opinion is NOT adopted.
Sunrise had a big success in robot anime.
For example: Gundam,
In 2007, Namco (the game company that created Idolmaster) finished acquiring Sunrise and merged executive members.
In that time, Idolmaster was one of the most successful games by Namco.
The executives gave an order to the animator team that created My-HiME to create an anime version of Idolmaster.
Animators at Sunrise were professionals of robot anime, they weren't fit to make idol anime, but they had a policy. Therefore, they created robot anime that used characters of Idolmaster.