Batman: Gotham Knight

Both are anime made up of shorter segments meant to explain the gap between feature films. 

You could say that "The Skull Man" is Japans dark heroes tale in comparison to America's "The Batman". If you like dark hero series then the one you haven't watched may be for you. 

Both are anthologies based on some source material and created by various studios and directors. 

Both of these shows have protagonists who are vigilantes who do not believe in killing their enemies.  

Both of these shows have protagonists who are vigilantes/wanderers who do not believe in killing their enemies.  

Both of these shows have protagonists who are vigilantes/fugitives who do not believe in killing their enemies. 

Batman and the Phantom Thieves do not tolerate killing and will bring criminals to justice that is better served according to their own standards. 

Batman: Gotham Knight is not hentai (well no duh), but these two anime have a similar dark feeling to them. They both have a superhero that patrols a dark and corrupt city with their own view on justice. They have enough action to keep you entertained. 

Both are co-productions between Japanese studios and western companies, meant to fit as parts of popular western media franchises. They feature mostly realistic artstyle (excluding parts of Batman animated from Studio 4°C) and high-quality, natural-looking animation. 

For a starter, both Wolverine & Batman are based on famous comic book characters, created respectively by Marvel and DC comics. The characters are also quite similar: both vigilante anti-heroes, who are struggle to cope with their dark past, while still keeping their human nature and will to do good. The stories also follow a similar path: both protagonists are usually seen fighting against groups of enemies while trying to save or protect someone. Overall, I found these two anime to be quite similar, not only in the characters are storytelling, but also in the mood they create and their visuals. 

Both feature characters who lead double lives to punish the bad guy and no one suspecting the person that is least expected is actually the alter ego that they potray too. 

Action OVA anime about superheroes that are both based on a western comic franchises. One is based on DC comics franchise and the other one on Marvel franchise. Both are not direct comic adaptations but rather kind of original stories. 

They are both based on popular American comic book series. 

Both series are dark and violent, done in a Gothic style. They follow the main character through death and mayhem that they are for some reason compelled to get involved in, one because he is dumped right in the middle and the other for psychological reasons. 

Lelouch (Zero) and Bruce Wayne (Batman) are very similar but in a different world, different style, different setting, and mostly a different universe. They have a strong sense of justice by becoming vigilantes and not heroes because they have used the concept "ends justify the means" to defeat evil. Also instead of using superpowers, they mostly use gadgets despite Lelouch uses a supernatural power geass (which is not an ordinary superpower but an optical eye power). They are both geniuses living a rich life with a partner along with advanced technology. However Lelouch and Bruce later faces a series of events that will forever change everything. Code Geass is more of a mecha than crime solving and fighting but if you find one similar to the other, watch it! read more 

Darker Than Black may be an anime but it has elements similar to superhero/detective/supernatural shows and Batman is one of them. Darker Than Black is a great addition to watch if you like Batman especially Gotham Knight because here are the similarities: -Hei and Bruce Wayne are on a double life as Black Reaper and Batman -Both deal with criminals -Both have partners -Both deal with crime scenes Differences: -Hei is employed by the Syndicate to eradicate Contractors whereas Bruce Wayne takes down criminals as a vigilante -Darker Than Black have supernatural powers and Batman deals with people with artificial powers 

This is an adaptation of the DC Comic universe, much better in my point of view than this Iron Man adaptation. Several studios - Bee Train, Madhouse, Production I.G and Studio 4°C - each worked on their own film in this compilation. 

A lot of ends justify means involved, action, masked vigilante trying to fight evil, gadget, same tone, different setting, suspense, and the true focus of the main character by showing his true character. 

The Big O's Roger Smith is pretty much Bruce Wayne with a super robot as opposed to a Bat costume. Much of the production staff behind The Big O had previously worked on outsourced animation for Batman TAS, taking much influence from that particular iteration of DC's rich superhero. Batman: Gotham Knight is a simply a more direct anime version - just from some different talent and an alternate anime studio involved.