If you're looking for manga similar to Demon City Shinjuku, you might like these titles.
When the zombie apocalypse came to Japan, Satou Masaru thought he was a goner for sure…until two super hot girls came to his rescue! But Satou’s relief is short-lived once he realizes just how insane his saviors are: Karin is a happy-go-lucky psycho, while Miki is a megalomaniac with plans to create an undead army and rule the world! Can Satou survive being their underling, or will he take his chances with the zombies?!
Miho, a woman of beauty, intelligence, and temper, comes to Cheju Island to teach school and is immediately flung into a world of terror and the supernatural. A demon attacks her, and she is saved by the chance appearance of a mystery man with seemingly only one mission: demon killing.
A girl with prosthetic limbs and a tragic past wanders a zombie-ridden 23rd century earth now known as Death’s Amusement Park. Overrun by monsters, the post apocalyptic wasteland is the last place a little girl should call home, but she’s developed a unique coping mechanism…
16 years ago, Japan was swept by a series of natural disasters that destroyed all modern society. Momoka lives with her grandmother who makes a living selling pieces of the old technology. It's Momoka's job to dig up the "treasure" from the junk yard. But, things get harder since some punk mutant(?) oni claim the junk yard as their own. The battle is on as Momoka battles the oni for a piece of the action with her friends Monkey, Dog, and pet bird, Kiji.
Benny Imura and his friends must navigate a post-apocalyptic zombie-infected America in which teenagers are forced to find labor or face starvation. When Benny grudgingly joins his annoying older brother Tom as an apprentice zombie hunter, he soon discovers that almost everything he believed about his sheltered life is wrong--and zombies aren’t the greatest thing to fear in the Rot & Ruin.