Synopsis: There’s never a dull day in Ikebukuro, a commercial district in Tokyo, Japan. Featuring a cast you’ll want to know (and will get to know) more and more in-depth, many characters have their daily run-ins with each other and somehow always manage to yield chaos. Though among others as well (think stalker girlfriends, “back-alley” doctors, gang leaders, and even a motorcycle-riding Dullahan!), the series takes a primary focus on Mikado Ryugamine, a boy who moves to an already unstable Ikebukuro attend school with childhood friend Masaomi Kida. Everyone has their secrets.
Similarities: Okay, going to admit, there are some big differences between Durarara!! and Blue Exorcist. Some similarities are they both focus on some supernatural; Blue Exorcist on demons, and Durarara!! on myths/legends.
6. Hellsing Ultimate
Synopsis: In a world where vampires exist, eating any prey that get caught in their fangs. Fighting against the undead is the Hellsing Organization, who dedicate their existence to destroy any who is a threat to humanity. Leading the Organization is Integra Fairbrook Wingates Hellsing, commanding a powerful military and fighting against the vampires. In her army lies the ultimate weapon, a vampire named Alucard. He fights against his own kind, as he obeys his commander. Alucard and his new vampire servant, Seras Victoria, must battle anyone who dares stand against Hellsing.
Similarities: Both series includes the main characters fighting against their own kind. Rin is fighting against other demons, while Alucard and Seras are battling vampires. To fight against demons or vampires, both series have the main characters in a setting specifically towards eliminating them (anti-vampire organization, and school of exorcists).