Nicococo!!

Nicococo!! is a four-part Durarara!! mini-series that takes place after the conclusion of the original series and serves as a prequel for Durarara!! SH. The mini-series was released for Niconico, a Japanese video-sharing site, in 2014 to jointly commemorate the 10th anniversary of Durarara!! and the 20th anniversary of Dengeki Bunko. It was included in the Durarara!! gaiden anthology.

Nicococo!!
Walker Yumasaki and Erika Karisawa barge into Celty Sturluson's home with plans to star Celty in a Let's Play video. Walker shows Celty a video of Erika singing in cosplay and reveals that she is a famous cosplay performer whose stagename is Eternal de Charmante. Erika has a rival on Niconico called Blizzard la Blizzadia who is friends with a famous Let's Play gamer, and the two cosplay rivals had agreed to have their friends each submit a movie to Niconico, with the one getting the most Mylist bookmarks winning the contest. Celty reacts angrily to their plan and declines with her personal safety in mind. Shinra offers to upload a collaboration of fragments of videos he has taken of Celty during the years they've lived together, and Celty agrees to help Erika to stop him.

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Having agreed to help Walker and Erika create a video, Celty is trying to decide on the best content to make the video successful. The most popular videos on Niconico are Let's Play, so Celty tests a horror game. One hour later, Shinra finds her hiding in the closet.

After he calms her down, shuts down the alien horror game, and convinces her there are no gray men around, he suggests they try playing a difficult game together, one made by their acquaintance Izaya.

The game is made to test the player's patience. Minutes later, Shinra is attempting to calm Celty as she fights the urge to smash the screen, and he reveals that the only one to have ever finished playing was someone named Tsukumoya, a stranger who reached out to Izaya with his thoughts on the game. Though Shinra had filmed Celty's reaction to the game, she decides that she should do something other than live reaction videos.

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Shizuo Heiwajima spots Celty filming on the street and the two discuss the peacefulness of the city and the rarity of people with special skills. He wishes her luck. When they part, Celty runs into Mairu and Kururi and asks them about the type of videos they like to watch online. Looking for more opinions to reach into the hearts of ordinary people, she heads to Russia Sushi, where Dennis and Simon propose she advertise for their restaurant. As she leaves, she runs into Akabayashi, who offers her a video saved to his phone, but when she hears the contents of the video, she runs away. She encounters Anri Sonohara on her way home from school and decides she would like to a make a cute and pleasant video, but she quickly discards the idea, settling for a video only she can make. As she is attaching her camera to Shooter, Kinnosuke Kuzuhara approaches her, and she flees. At some point during the two-hour police chase that ensues, Blizzard la Blizzadia's friend records the scene and uploads it to Niconico, where it rises high in the rankings.

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Shinra comes home to find the apartment full of shadows and Celty depressed over the idea of losing Erika's competition. Shinra attempts to cheer her up and helps her formulate a plan to get the two rivals to reconcile. While watching Blizzard la Blizzadia's videos, they recognize the performer and contact Kyouhei Kadota to force the two rivals to meet. They apologize to each other in person and release Celty from the responsibility of creating a video.

Several days later, Eternal de Charmante, Blizzard la Blizzadia, and her younger sister Homura-chan host a live show on Niconico together, where they announce they will do a Let's Play of a game created by Blizzard and Homura's older brother. Celty, screaming internally, types a warning in the comments.

Cultural References

 * Niconicodouga is a popular video-sharing site in Japan. On the site, users can bookmark videos they like using the feature called Mylist. The number of Mylists a video has is readily available information, along with the number of views and comments.
 * Let's Play is a type of video that provides a walkthrough of a video game with player commentary. The focus of Let's Plays is more to provide entertainment than guide viewers through the game. This style of video rose in popularity online in the late 2000s and early 2010s.
 * Mahjong, referenced by Celty when she asked Erika why she and Blizzard couldn't have decided on a simpler way to settle their spat, is a tile-based game for three or four players with great popularity in Eastern Asian countries.