touhou and *misaka
Touhou is a bullet-hell series made by one man (that I call God), ZUN. The series is famous for three main aspects. The game itself, the music(my favorite part), and the giant universe and intricate backstories/relations each character has with one another. Going off of the third point first, touhou is actually on the guinness world book of records for most prolific fanbase ever. This is primarily, in my opinion, due to the fact that canon and fanon co-exist with each other and with literally a hundred characters with a dozen major settings + three manga series + other informational books (Bohemian Archive in Japanese Red comes to mind), there is literally no end to the fan-made material you can produce. Going off of that, the music part is also amazing. There are about 200 official tracks with their own distinct melodies and "theme songs" for specific characters (some characters have multiple. Eg, Kirisame Marisa has 6 themes) make it possible for musical people (like me) to make an endless variety of musical arrangements either based on characters you like, by the game the songs were released in, other canon/fanon groupings of characters, or just a random clusterfuck of songs that sound epic. Finally, the game itself is great for challenge lovers. Just
watch this video for a perfect example of "challenge." (By the way the songs in that video are Extend Ash ~ Hourai Victim followed by Reach for the Moon ~ Immortal Smoke)(I have almost every song memorized by now)
I could go on for another 50 pages about touhou but I'll stop there

(And Misaka is from To Aru Kagaku no Railgun)