Devilman Crybaby
My introduction to the Devilman franchise, which has been around since the 70's.
It's a really dark, for-adults anime. Everything including gore, profanity, sex and nudity covers this series.
I found myself invested right away. The animation is stunning and stylish, showing off the modernized design of the demons really well. The music really bops, making some moments feel epic, others depressing, or even sweet and light if it needs to be.
I can see the Devilman story inspiring works like Neon Genesis Evangelion.
Overall, great short anime that instantly made me a Devilman fan!