Characters who in universe are anime fans of anime that actually exist in real life and weren't made up for the show

You aren't going to find too many examples of this because of copyright issues. Usually they change the name a little, like Precure to Prepure. The reason Konata could be an open fan of Haruhi was because Kyoani had the rights to both series.

@Subarctic-Forest
It is unfortunate that such free advertising is rejected. I have read multiple books I otherwise wouldn't have, after hearing fictional characters profess a love of them. In America, at least, titles can't be copyrighted.

@Lucifrost
Might be a cultural thing in Japan vs the US. In America the idea that there's no such thing as bad publicity is huge, probably not the case in Japan.

@Subarctic-Forest
I don't believe the legal rationale has anything to do with publicity. You can title your movie "One Piece" and get away with it here, provided you write an entirely original story with no connection to Oda's.

@Lucifrost Perhaps if "here" is the moon. You're unlikely to on Earth. Mainly because that would be a trademark infringement which must be procecuted or risk loosing the trademark.

@therealnagora
Not if the title hasn't been trademarked. It's difficult to trademark a title.

@valico Ah, was not aware of that, i just remember clips showing up in the show

Well they were referenced as games but also could be understood as anime -> Persona, Stein's Gate and Akiba's Trip in No Game No Life [Sora's original world], aswell as they used Laputa spell from Flying castle movie. It was very open that Sora and Shiro are familiar with anime, video games and even H-anime games so it shouldn't be a surprise. Also almost forgot they wanted to quote Jojo and did which was among their most wanted lines they wanted to say out loud, so they are 100% jojo fans.
Some popular donghuas are seen in My ACG Parents alongside with cosplays made for them [I've only recognised Tian Guan Cifu, Bai Yao Pu and Daily life of immortal king, but there's way more titles] - The MC is familiar with them, but her parents are donghua fans.
Bleach, DB, Naruto, YY Hakusho in Jujutsu Kaisen as Yuji referenced them - maybe not a fan but we know he watched them.
Erika Karisawa and Walker are often found with light novels so they are Sao fans, for example in Opening 2 of DRR you can see Sao's first volume, while somewhere at the beginning of the show you can see them walking with a cardboard layout of Holo from Spice and Wolf -> I don't remember if there wasn't by any chance a small conversation about their favourite light novels/anime.

In this opening in 0:52 when you pause before Kadota's face [after Erika's introduction and that buddy] you can cleary see Sao first volume Light novel, there's few more but I am not that familiar with Light Novels/Mangas. I only recognise Sao cause I've read them myself.

@Zettaiken Kadota whole gang is based on Kadokawa authors, and both Erika (she compares Saiya to Shakugan no Shana) and Walker (he poses with Spice and Wolf Holo, among others) torture methods are based in anime.

Well they were referenced as games but also could be understood as anime -> Persona, Stein's Gate and Akiba's Trip in No Game No Life [Sora's original world], aswell as they used Laputa spell from Flying castle movie. It was very open that Sora and Shiro are familiar with anime, video games and even H-anime games so it shouldn't be a surprise. Also almost forgot they wanted to quote Jojo and did which was among their most wanted lines they wanted to say out loud, so they are 100% jojo fans.
Some popular donghuas are seen in My ACG Parents alongside with cosplays made for them [I've only recognised Tian Guan Cifu, Bai Yao Pu and Daily life of immortal king, but there's way more titles] - The MC is familiar with them, but her parents are donghua fans.
Bleach, DB, Naruto, YY Hakusho in Jujutsu Kaisen as Yuji referenced them - maybe not a fan but we know he watched them.
Erika Karisawa and Walker are often found with light novels so they are Sao fans, for example in Opening 2 of DRR you can see Sao's first volume, while somewhere at the beginning of the show you can see them walking with a cardboard layout of Holo from Spice and Wolf -> I don't remember if there wasn't by any chance a small conversation about their favourite light novels/anime.

In this opening in 0:52 when you pause before Kadota's face [after Erika's introduction and that buddy] you can cleary see Sao first volume Light novel, there's few more but I am not that familiar with Light Novels/Mangas. I only recognise Sao cause I've read them myself.