Kabaneri of the Iron Fortress

In a steampunk reimagining of Japan, the remnants of humanity survive in fortress stations connected by armored trains, because the world outside is crawling with Kabane — undead creatures whose hearts are coated in iron, making them nearly impossible to kill. Think steampunk Japan meets zombie apocalypse. Ikoma is a young engineer who's been quietly building a weapon designed to pierce those iron hearts, and when the Kabane breach his station, he finally gets to test it. The catch: he gets bitten in the process. Instead of turning fully, he somehow stops the infection partway, becoming a Kabaneri — a human-Kabane hybrid with enhanced strength but still holding onto his mind. He ends up on a fleeing locomotive with a ragtag group of survivors, including Mumei, a mysterious girl who turns out to be a Kabaneri too. From there it's a 12-episode sprint of desperate survival, trust issues between humans and the hybrids trying to protect them, and some genuinely gorgeous action sequences. Wit Studio animated this right around the same time as Attack on Titan, and it shows — the production quality is sharp, the choreography hits hard, and Hiroyuki Sawano's soundtrack does exactly what you'd expect from the guy who scored AoT. If you liked Attack on Titan's walled-civilization-under-siege setup or wanted something like Seraph of the End with tighter pacing and better animation, this is worth your time. It's dark, it's gory, and it doesn't waste episodes getting to the point.