I noticed both their PVs had stories to them having to do with popularity/and/or record companies. They are really similar in details, but generally are the same types of stories about rising and falling:
alterna=Exploiting record company and hounded by the media, the human side of her is thrown out and replaced with "the Signing Machine", but still has her passion for music.
Negaigoto=Popular w/ Sony, thrown out like Ayu, replaced by new people, discovered and has an even bigger comeback. Oh poo, her first single that isn't ___ful.
I don't care about copying, they are in the same record company anyway, but it's strange that the supposed rivals are both making PVs that are very different, yet similar in overall stories.