The story is a mystery about a green cat and a private detective who investigates where it came from. The cat was thought to be good luck, but eventually brought misfortune to all those who come in contact. The story was taken directly from the 5th subtitle of the 1950s Lion Books manga.
tl;dr: It’s an okay OVA. If you have extra time on your hands, go ahead and watch it.
Midori no Neko is one of the most mediocre OVAs I’ve ever seen. It’s not what I would call “bad”, but it’s not good either. The characters were pretty boring, with the old PI being the only one I could kind of relate to. The plot had several holes in it, seeming to change as the story required, and the art and music was just dreadful, although this could be justified since it’s from 1983.
The story revolves around this old man
who’s name I forgot (he was that unmemorable). He’s trying to find his friend’s son who was possessed by this green cat who’s actually an alien but actually a god who gives you good fortune all the time. If that sentence made no sense, well, you and I are in the same boat. Most of the story is told in flashback from the perspective of the old man and his journey to find his friend’s son. It’s a pretty good idea for a story, especially when it’s just an OVA and not a 13+ episode series. There’s a few major twists in the series.
The first is that the green cat in the story is an alien from outer space and it only LOOKS like a cat to humans. It’s “true form” is a purple, anorexic-looking alien cat. The second twist is that the greenness or the cat is because of chlorophyll. You know, that stuff that plants use to collect sunlight and carbon-dioxide. You’d think that this would mean that the cat needed sunlight in order to live/grow, but nope. I guess it’s a special kind of chlorophyll that only needs carbon dioxide but not sunlight, since the cat spends a lot of time indoors. Also, it was stated earlier that the greenness was just a disguise and the true form of it was a purple alien cat. See what I mean when I say there are major plot holes in the story?
As for animation and sound, it’s nothing special. It looks and sounds like any other anime from that era. The voice acting was pretty bad and the sound effects were pretty bad, but this was from Astro Boy era, so yeah. Overall, the anime was okay. As I said before, not very good, but not terrible either. Is it worth watching? Sure. It’s only 20 minutes long, not including opening and ending credits which are extremely boring and skippable.
If you stop and think about it for a minute, most of Osamu Tezuka's stuff is a little bit out there. As in, some pretty unusual premises to get the story going. But this short little one-shot story takes that one extra step.
Alien green cats befriending and twisting young children? Yeah, that's pretty weird.
But, whatever, anime is filled with some of the strangest story concepts out there. Let's roll with it.
They really crammed this story into as short a time as possible, with lots of very quick
cuts and time skips. The artwork is perfectly fine, on par with what you might come to expect from any other Tezuka work. The plot, well, it's a quick story, and not a particularly interesting one at that. With the quick pace of the storytelling, it just sort of rolls past, and before you know it, the tanks are rolling home, and it's over.