Origional Video Animie. Sort of like the "only on video" sequels from Disney.
It just doesn't pay the sweatshops that churn out these animie to finish the story. As long as there is no final chapter then they can shove in all the omake (extras) that they want without the broadcasting commitment.
Which, I trust, continues to pull in royalties for Takahashi-Sama. At least in American publishing it would. The bad old days of a creator's sponsored work becoming the sole property of the sponser are slowly becoming a thing in the past.
However, anything (and I do mean anything) in the animie that is not true to the manga is just omake. The studio gives her a great deal of credit and asks her advice but they do not have any obligation beyond leaving the main storyline alone and not killing anyone she keeps alive. That's why the animie relationships aren't really like the ones in the manga.
That's enough class for today...
