If you're looking for manga similar to Attack on Titan: No Regrets, you might like these titles.
In the holy land of Nostralgia, isolation is the norm. Surrounded by a towering wall and a waterfall, its citizens are forbidden to try to climb the waterfall, for only demons live outside and leaving will bring a great calamity. Milo is a talented machinist who lives in Nostralgia and pines for her fiancé, Albert, who broke the law and escaped to the outside world years ago. She longs to find him someday, and when she finds a strange machine in the water that says its name is Edison, it seems that Milo finally has her chance...
A floating ring has been passed down through Mikko's family for generations. Her grampa told her that the ring bears a promise of reuniting with lost ones who departed to the "other world." Mikko explores her world -- an endless network of tunnels -- in hopes of finding the "other world" one day...
Long ago, angels and demons engaged in a fierce war; and to keep humans safe, angels built the city of Ilvia. In the center lies a walled sanctuary where special children must live until their fourteenth birthday, at which point they graduate and leave for paradise with Amalda, their angel caretaker. Akira, Yuno, and their friends are about to turn fourteen, and their curiosity leads them to sneak outside of the walls for a peek of paradise, not realizing the horror of what awaits them...
The remote town of North Hill has been quarantined to prevent the spread of the mysterious Couper disease that is turning people into cannibals. Young soldier Billy returns to his hometown for the first time in six years for the woman he loves, but what horrors will be awaiting him...?
A child yearning for freedom is stuck behind the massive walls of the city controlled by Mozgus, a cult leader. The Cult claims that there are only terrifying monsters outside the walls, but...
Set in a ruined world overrun with chimerical creatures where the female creatures eat the males. Two creatures explore the land: Usagi, the elder sister, protects her brother Mitsuki, a curious chronicler who is able to read the books in their secret hiding place to know that the world was once different.
Emma, Norman, Ray, and many other "siblings" live at an isolated orphanage cut off from the outside world. They live a charmed life surrounded by friends and watched over by Mama, their caretaker, until they leave the house for a foster family by the age of twelve. The only rule is that they must never venture outside of the gate that isolates them from the rest of society, for dangers await. But one day, the children learn the true horror of what's in store for their short lives...
A race of "succubus" that breeds human beings in the nursery, and human beings trying to eradicate them. After an eternity of time has passed since the two incompatible races began to fight, a "king" will be born who will end the battle.
The Flame Dragon Knight traces the rise of the warhammer-wielding warrior Grunbeld from humble beginnings to become the all-powerful Apostle who will one day face Guts in mortal combat!