This OVA should not exist. Given the excellent and emotional ending of the parent series this is just out of place and makes no sense as "episodes 25/26". I personally hate when anime do this; just leave well enough alone and leave the ending of the story where it is. I guess if you are looking for more story it is not the worst but it just really messed with me after coming off the very strong ending to go WAAAY back in the story to when everything was still normal. It would have been far better to add this as part of the seriesproper instead of ramming it in at the end.