This OVA is a short snippet of Natsuiro Kiseki's four main characters four years after the events of the TV series. It shows them meeting up at Rin's shrine for the first time in a long time, where they have a short conversation about what they've done since the events of the main series and what they will be doing with their futures.
I hate OVAs that are purely fanservice or are unrelated to the original storyline--this is definitely not either of thoes things. It is short'n'sweet, and adds to the storyline by giving us an idea of what came after.