Additional Content

Some content has been made to promote Catulus Syndrome. Since there are no official English translations, these were only targeted to a Japanese-speaking audience.
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==Vocaloid song "Cat Ear Complex"==
On 2017-10-27 a vocaloid song "Cat Ear Complex" was released.
==Short animated adaptation of Chapter 3==
On 2019-06-07 a short, 30-second adaptation of Chapter 3 was released.
==Artbook Crowdfunding Campaign==
On 2021-03-14 a crowdfunding campaign to print a limited Catulus Syndrome Artbook finalized, having raised 19.8 million yen, almost 10 times it's set target of 2 million yen.https://twitter.com/nekotarou0721/status/1350096653752135683https://camp-fire.jp/projects/view/372455
The artbook included some of the illustrations drawn by Nekotarou up to that date. Other tiers included tapestry of the artwork; an additional handwritten signature from Nekotarou; and a custom illustration of one of the characters, limited to only 5 backers.