Seinen is my jam too. I recommend Golden Kamuy and Dorohedoro. The first is a historical fiction piece based in the early 12th century Japan with a fantastic story, great characters, and some unexpectedly outrageous humor. It kind of doubles as a food anime sometimes too, then it pivots back into the drama and action at the drop of a hat. The second is a story about a man whose head got turned into a lizard's and he's trying to find how to reverse the magic and find his real head. But there's also crazy magic users, a giant cockrock guy, devils, and gyoza. Everyone looks like the biggest edgelord, but they're all just a but of goofy idiots. It's the best. Also the soundtrack kicks ass.
That was the absolutely worst description of those shows. I AM VERY SORRY.