This has been a anime on my watch list for a while but I never got around to it but if the main series is as good as the OVA, I'm in for a treat.
If you like bittersweet ending, you will probably enjoy this one a lot. This is assuming if you plan to watch these first like I did. I don't regret it like the man full of regrets. I think it's a good way to set up and get you excited to watch the main series. They stand along on their own and it is a beautiful telling of a story.
For a OVA it captures so much story and plot in just 3 episode compared to most other shows with a lot of episodes. It did a wonderful job of telling a beautiful story start to finish in 3 short episode and I say, it's worth a watch!
