Firstly, I’m aware that there’s already a thread for this, but it’s almost a year old and didn’t really go anywhere other than linking to an archived Trello card, which seems to be abandoned.
Having support for anime series, Sonarr needs to support a decent database for it. TheTVDB is awful for anime, even listing some episodes in the wrong order, or listing episodes from the main series as specials. A great example for this is the Monogatari series. It’s completely f*cked.
First of all is the fact that it’s listed as a single series (called Monogatari), rather than its seperate seasons (Bakemonogatari, Nisemonogatari, etc). That’s not a big issue, and it’s actually quite helpful for remembering the watch order in Plex. That is, if TheTVDB actually listed the episodes in the correct order. It lists Tsukimonogatari and Hanamonogatari as “Season 0”, when they should be seasons 4 and 5 respectively. This wouldn’t even be so much of an issue if it was possible to find any downloads for these episodes - but none are listed, as uploaders are using the correct naming scheme, so there are no results for “Monogatari S00E03” or whatever it’s searching for.
There are several other series that have this issue, but so far Monogatari is the worst offender that I’ve found. As somebody pointed out in the previous thread, it’s entirely possible to use a different database for anything listed as Anime, using the HTTP API of AniDB.