Gunslinger Stratos: The Animation is an anime television series adaptation of the Gunslinger Stratos video game series.
This anime exist in two version - "L" ("TV", originally aired on TV and Crunchyroll) and "R" ("Web", originally aired on Daisuki and Niconico). Only episode 12 is drastically different, but most other have very subtle differences (like a car is present on a street in one and not in other, slightly different line is spoken in dialogue, etc) and there exits an explanation from authors how all this little differences led to a different outcome in ep 12.