These Underrated Anime Opening Themes Have Never Gotten Enough Credit

Durarara!! has five different openings that are fantastic, but the very first OP is often overlooked in favor of "Complication" by THE Rookiez is Punk'd. Durarara's openings are unique because they make it a point to help the audience keep track of what's happening. This song by Theatre Brook is just pure fun and sounds like it belongs in Ikkebukoro, and is definitely worth a shot to listen to again. 

The Devil Is A Part Timer is literally about Satan going to work at a McDonald's-type restaurant while dealing with his demon roommate, a girl who wants to kill him, and his teenage coworker who's in love with him. The opening theme song is sung by popular singer Minami Kuribayashi, who released this song as her 31st single. The song is pure fun and the opening theme shows that even all-powerful angels and demons don't know how to navigate the world as adults. 

Aldnoah ZERO is an anime where the villains have the cool mechs, not the heroes. That leaves protagonist Inaho to rely on his intellect to defeat enemies. This opening is sung by Kalafina, the artist who's contributed to the soundtracks of anime like Madoka Magica and Fate/Zero. The soundtrack itself was made by Hiroyuki Sawano of Attack on Titan fame. The song is quite solid, but doesn't get the hype it deserves. 

The Future Diary is an incredible anime that keeps you guessing every second you watch it. The opening theme is no exception to that rule. The song is incredibly catchy and far superior to the second opening. Once you watch the first half of the series, everything about the opening falls into place. The opening basically lays out the story for you, but in a vague enough way that the twists are still a surprise. 

Free! is by no means an unpopular or unknown anime. However, this song is interesting because it's sung by OLDCODEX, a band whose frontman is the seiyuu for main character Makoto Tachibana. He also sings the opening song for Free! Eternal Summer, the second and final season of the show. All five main actors for the Japanese subtitled version of the show sing the closing themes for both seasons under the band name STYLE FIVE.