Seraph of the End: Vampire Reign

When a mysterious virus wipes out every human over the age of 13, vampires crawl out of hiding to claim the surviving kids as blood banks. That's the world Yuuichirou Hyakuya grows up in, penned underground with other orphans, kept alive only because they're useful. He and his closest friend Mikaela refuse to accept it, and their desperate attempt to escape goes about as badly as you'd expect. What follows is Yuuichirou clawing his way into humanity's last military force, driven by grief and a need for revenge that borders on reckless. The Japanese Imperial Demon Army fights back against vampires using cursed gear: demonic weapons that are almost as dangerous to their wielders as they are to the enemy. It's a 12-episode TV series from Wit Studio, the same team behind Attack on Titan's early seasons, and you can feel that pedigree in the fluid action sequences and the weight of the world-building. The soundtrack leans hard into the bleakness, which fits. If you liked the desperate human-vs-monster tension of Attack on Titan or the darker emotional beats of Tokyo Ghoul, this hits a similar nerve. There's also a Blue Exorcist vibe in how it handles chosen-family dynamics and supernatural military structures. The bond between Yuuichirou and Mikaela is really the emotional core here, everything else, the battles, the politics, the power system, orbits around that relationship and where it fractures.