Some are actual independents, but others are small, regional parties.
I think Tax Cuts Japan managed to win a couple seats, and Okinawa Mass won a constituency seat.
The independents tend to be pro-LDP or pro-DPJ. I think there are 3 pro-DPJ indies and 4 pro-LDP indies.
According Japanese Wikipedia, the 8 independents elected were:
Kishirō Nakamura: Former Liberal Democrat, former Reform Club (proto-New Renaissance Party)
Koizumi Ryuji: Former Liberal Democrat, former member of LDP rebel faction led by current Party of Future Generations leader Hiranuma Takeo.
Keiichiro Asao: Former New Frontier, New Fraternity, pre-1998 Democrat, and most recently Your Party member.
Kotaro Nagasaki: Former Liberal Democrat
Tsuyoshi Yamaguchi: Former Democrat
Kamei Shizuka: Former Liberal Democrat, People's New, Tomorrow, and Green Wind Party member.
Takahiro Inoue: Former Liberal Democrat (Aso faction)
Nakazato Toshinobu: No Wiki page.
Sorry, too lazy to change naming order.
Anyway, I don't think anyone was elected from Tax Cut Japan unless the guy without the Wiki page is. Don't see anything about the Okinawa Social Masses Party either. Maybe you heard that a leftist had been elected in Okinawa and assumed it was them. It was actually a Communist that won Okinawa, apparently the first FPTP seat they've won in a while (ever?).