Vinland Saga- A great viking/christian/philosophy story with lots of really well-done characters and even the background characters look 100% different from each other, so it feels really weird looking at the panels because it's so good. We follow Thorfinn who goes from a naive kid to hate incarnate and then a souless husk and then finally nice guy pacifist.
Vagabond- What is there to say about this? I can't explain the appeal of this one tbh. It's just good samurai stories
Ajin- It's about people who respawn and have ghost demons that aren't super reliable but really handy for shit other than fighting. They don't respawn, they can just never die. If they break their leg for instance, they will live with a broken leg, but if they die, they come back with a healed leg. Everything just resets. I love this manga because its strong points aren't compelling character drama, or philosophy, but rather about the main guy who's a genius and almost emotionless and his friend vs these few Ajins led by Satou. Who's Satou? He's a guy who made special ops back in the day. He and like 3 other went into an enemy stronghold place in Vietnam during the war, and rescued a prisoner without anyone noticing. Satou thought that was boring however, so he shot his gun and alerted all the vietnamese in the area. Satou's an unpredictible genius that just raises the stakes all the time. He's a force of nature. I want to say some of the crazy shit he's doing in the series but I don't wanna steal that from you. It's Japan vs Satou, and Satou essentially wins but the manga isn't over yet.
Firepunch- story about a guy that can heal all wounds really fast, but unfortunately for him he also kinda got burned by a fire that can never be put out until it has exhausted the thing it burns, so he burns for like a few years or something and can't do anything about it, but slowly he's able to do things like walk and deal with the pain. He goes on to walk the earth, a human torch. The fire that's burning him never gets put out, so if the fire touches another person that person will burn until they're dead etc. He lives in a world of eternal winter.