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C2 Kikan (Japanese: C2機関/株式会社C2プレパラート (C2 Präparat Inc.)), alternatively translated as "C2 Architecture", "Contents Communication Architecture", and aka "KanColle Unei Chinjufu", is a doujin circle, who is one of the copyright holders of the Kantai Collection -KanColle- brand.
C2 Kikan debuted in Comiket C75 (Winter 2008) with a doujin about food, introducing various types of food through anime personifications. They were interviewed by various TV programs for it at the time, including タモリ倶楽部 from Asahi TV and MAG・ネット from NHK. They later published several military-related doujinshi.
It's possible that the name of 'C2 Kikan' came from Final Fantasy: Unlimited, where Tanaka Kensuke, one of the main members of C2 Kikan, was the anime's general producer for, when he worked in Square Soft back in 2001.
When Tanaka Kensuke and his friend, who was working within Kadokawa Games talked with Michio Okamiya, whom he once worked with back in Square Soft, they came up with the idea of the KanColle browser game.
(Source: KanColle Wiki)
Official website: http://www.c2architecture.com/
Official twitter: https://twitter.com/C2_STAFF
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