cannis

that does sound like a good idea: i've considered making something like that in the past but realized i'm not quite knowledgeable enough on javascript yet to make it a thing, but i'll definitely keep it in mind. it would also be nice to be able to create a page for each series automatically based on some sort of template and automatically fetch metadata, though i'm not sure how that could be implemented

exactly, i think something like this would work best as a plugin or addon, though none seem to exist atm

i could be wrong, but aren't libraries intended to be separators for different types of media? in the jellyfin docs on libraries it directly states mixed media libraries are discouraged due to incorrect metadata. collections do sound like a good idea, but it lacks the visual and information aspect about the series i'm looking for. still, it does sound like the best choice so far

the specific artbook of the picture you posted is available on archive.org with the title "evangelion material", you can download it separately with the torrent they provide. the internet archive actually has a pretty impressive artbook collection, though i actually found that specific file under a mirrored torrent on one of the dht search engines on the megathread, which are surprisingly helpful/extensive, though a lot of torrents (especially older ones) aren't being seeded, but it's a good start once you have the filename.

as for non-english forums, i've had luck with baidu search: you'll be mostly looking for pan.baidu links in animanga forums/sites (which may be hidden behing login walls, but most of the time you can use google's cache view), though you do need an account to download from them, which can be difficult to get depending on your location. one specific forum that seems to have a lot of content not available elsewhere is otomedream, but it's 1) very difficult to get in, i've been on the waitlist to get my account approved for like two months; and 2) requires you to use their currency to get dl links to the actual content. also worth checking out is vk and japanese+chinese torrent aggregators and book download sites, fmhy has some in their non-english section. in most of these, you'll have the most luck searching the original japanese title in quotation marks.

i can't personally attest for private trackers like bbt and ab, but i imagine it's worth checking out if you have an account.

did you ever figure this out? i'm kinda in a similar situation, though i ended up just using a downloader for the clip studio online reader they provide

you're welcome, also leaving it here in case anyone needs to download something and don't have a premium account or trial:

this (https://scribd.vpdfs.com/) is the only site downloader that worked for me: it says that book and audiobook downloads are only available to beta testers, but when you input a book link it gives you the option of downloading the pdf or epub through zoboko.

not sure if it works for all files, and the formatting was a bit off when i tried it, but the content is all there.

doesn't seem to have any reference to a limit, so as long as you have an account with access to the books/docs you should be able to download them