Originally, Black★Rock Shooter was a character created by an artist known as huke, among plenty of other material that he uploaded to his Pixiv profile. One fateful day ryo, leader of Vocaloid synthesizer band Supercell, approached huke to create a song after having been inspired by his work, while also inviting him to join the creative team of the band. This way, the two collaborated on a music video, with huke making some small adjustments to Black★Rock Shooter's design and creating the version known today.Once uploaded on Nico Nico Douga in 2008, and soon after on YouTube, both the song (preformed by Hatsune Miku) and character became a massive success (on the internet anyway).
Tropes found in the original song and illustrations:
Adaptation Expansion: And how. From a drawing of a girl to a Vocaloid song to a 5 minute PV to a 50 minute OVA with backstory and names and, meanwhile, an RPG game, then a manga, then a companion anime series to the OVA.
Alternate Continuity: All adaptations take place in their own universe, with only the character patterns and general personality being constants.
Astral Checkerboard Decor: Almost all of huke's drawings take place in some checkerboard landscape. In one part of the PV, the sky is checkerboard.
Good Scars, Evil Scars: B★RS has two very prominent scars. One on her right hip, stretching from right above her pelvis around towards her back and a smaller straight one right below her left breast. Both scars are somewhat stitched up looking.
In Name Only: An interesting case with the adaptations in that it's not so much They Just Didn't Care, but there's so little information provided about anything in the original PV that the interpretations become widely diverged from each other.
This is taken to it's logical conclusion in Project Diva F, where the last note is always a Star Note in the middle of the screen, in the exact same spot as a white star appears on the video itself.
The Not Remix: The 2M Mix, made to commemorate the original version having been downloaded over 2 million times, contains redone vocals and instrumentals, but follows the same structure as the original. Additionally, the song, along with the other songs Supercell initially released on their website, was tweaked for the studio release of their debut album.
B★RS / DM / IB★RS, and even before the animated movie, B★GS. Though it appears STR is receiving much fan attention as well. However, it is the mentioned four who continue to overshadow B★M and B★DG, even though the illustrations of Black★Matagi and Devil★Girl were uploaded a mere few weeks after Black★Rock Shooter.
Speculation wise it is likely the said three were designed around the same months, with the release of the song being the contributor for the titular characters popularity.