This OVA adapts the1-volume manga called DOGS, by Miwa Shirow. The story continues in DOGS: Bullets and Carnage, which is still ongoing. There is also a short spin-off called DOGS: Hardcore twins.
The OVA has 4 episodes and each of them shows the story of one of the 4 protagonists, which take place in the same city. The city isn't named, but it's a big metropolis with a very active underworld. But there is also the underworld of the underworld, which is being explored in the Bullets and Carnage manga, and is just briefly mentioned in the last episode of the OVA.
The first OVA shows Mihai, a retired mafia hitman. He's back in town after many years and ends up having to deal with the unfinished business he left, mostly involving the son of a mafia boss that used to be under his care.
The second episode is protagonized by Badou, a very clumsy (but efficient) private detective who can't live without his cigarettes. During and accident while taking photos of an adultery, he discovers the secret of the boss of one of the city's syndicates and ends up being chasen by his underlings, But during the pursue his cigarettes start to run low...
Naoto stars the third episode. Her parents were murdered by people with swords when she was little and she herself was wounded, resulting in a X-shaped scar in her chest. But one of the killers rescues her and teaches her how to fight while she tries to avenge her parents.
Finally, we have Haine's story. This young man has supernatural endurance and acts in the towns underworld. One day, he sees two men chasing a young prostitute, a common sight in the city. But then he notices that she has two little angel wings and ends up saving her. He then must deal with the owner of the brothel from which the girl escaped.
This pretty much the plot of each episode. The interesting thing is seing how the stories are related, with places, characters and even protagonists showing up in the stories of the others. The gun and sword fights are cool, despite the infinite ammo and the stormtrooper syndrome.
The animation is good and the backgrounds are very good, depicting the city, virtually a character itself, very well. The character desing is faithful to the original. The soundtrack is ok as is the voice acting, except when they spout random english, ruining some scenes. But this is the writer's fault.
The characters are cool and interesting, but the OVAs are too short to develop them beyond the initial concept. The plot is interesting even though it's short and in the end you want to know more about the characters and the city. Thankfully, there's the manga. A good call on action anime.
What about the manga?
Miwa Shirow's character designs are good and stylish, but she can't draw backgrounds and the manga is full of simple or blank backgrounds, just like Bleach. In fact, she has many things in common with Bleach's author. She likes to do two-pages spreads and is more concerned with making the characters look cool in the fights than with the mechanics and the fluidity of the movements.
The main plot about is the real underworld of the city, a real underground labyrinth that has something to do with all the main characters, specially Haine and his regenerating ability, since the underworld is populated by genetically altered humans. Sadly, she couldn't keep the good work did in DOGS in its sequel. Maybe it's because DOGS's plot was simpler, but Bullets and Carnage's plot is confusing. And no, it isn't complex. She just doesn't conduct the story well.
Another problem is the huge focus on Haine, a stereotypical antisocial protagonist and Naoto, who is cute and cold, but not cold enough to be badass. Badou and Mihai, the funniest and most interesting characters become supporting characters.
The single volume manga that started the series and became the OVA is good, but its sequel doesn't have the same quality. The author has good ideas, but until now could't use them to stand higher than the average manga.