● I would like to start by saying that this is a spoiler-free review. I've read the manga and watched the 2019 OVA. The manga holds a dear spot in my heart, and I would like to say the same about this animation.
● Although this animation is considered a "longform anime" project that was bundled with an extra volume. I really doubt that many people will consider this when they just see this movie online, and for those people, I will consider the point of view of someone that hasn't read the source work.
The story covers Sensei and Shiva. An Outsider and An Insider trying to survive together while he can't touch her to not spread the curse. That's the same thing proposed before in both the manga and the first OVA.
Now covering the story of this specific animation, I can say that it is very weak. There's a real lack of context. Many important scenes and even arcs are totally ripped apart in this animation. Which is totally understandable given the fact that they're trying to cover a very dense 53-chapter work in basically 1 hour of screen-time. But the lack of facts takes away any trail of thought about what is actually happening while the story moves forward. There's no explanation of what is happening in the world, no real indication of background unless you consider the first minute and half of the movie (which you will only understand if you read the manga).
That is without a doubt the peak of this animation. The art style is absurdly good. It feels like you're watching an oil painting at times, with some charcoal sketches at others. It's very different from the first OVA and very different from any kind of work that I can remember from the top of my head. I won't be using a lot of images on this as it could spoil the little story that the animation has.
The scenes are literally breathtaking and, combined with the amazing soundtrack focused on classical piano to set up an emotional background, it just fits exactly as it should. If you consider the manga, it lacks a few aspects of a thriller, but it is undeniably beautiful.
As I said, the story isn't very well developed and you can't grasp the mentality or ideas of the characters very well. Particularly of Shiva, as it lacks a major arc.
If you're like me, you skip everything and read only the conclusion because you don't want to get spoiled with other themes. So I will try to be brief on this point:
If you're planning to grasp the idea of the manga by watching this OVA, don't. If you've already finished reading the manga, then you can definitely watch it and enjoy Shiva and Sensei.
It's unfortunate to think that there's maybe a good number of people that got hooked by the first OVA and went to read the manga so they could fully understand (my case). But I feel that if a clueless person watches this work, they will just get a feeling of nonsense and probably not consider the possibility of reading an amazing manga.
If you watched and didn't understand anything, don't worry. You're definitely not alone. Read the manga.