Sounds more like a 16-episode production, with the last 5 being 12A, 12B, 13, 14, 15.
-Joe
As reported on Sankakucomplex:
Interviewer: The announcement of the series’ 15-episode run was made at yesterday’s “Ore no Imouto Festival”, but could you summarize it for us again?
To put it simply, there will be two versions of episode 12.
During episode 12, there will be a divergence (in the story’s route).
One of those versions will be the “Good End” that will be the TV run’s final episode.
Then, there will be another episode 12 that will continue until episode 15 and will be a new final episode.
What was the reason for choosing such a way to end the series?
Originally, it started with the desire to have people who watched the full 1-cour (standard 3-month ‘season’) TV series until the very end to think “That was a really good final episode!”
Then, the plans for the TV ending began to take on the shape of an eroge-like route system (wherein the player has access to many multiple endings.)
This (eroge-like split ending) idea actually fits in very well with the spirit of the original work, and so we hope that viewers can feel that this is very much “Ore no Imouto~”.
Regarding the distribution schedule of the new episodes 12-15, has the time and release date been set?
The specifics are entirely undecided.
NSFW
Ore no Imouto Producer: The Anime Has Multiple Endings