Hagure Yūsha no Estetica (はぐれ勇者の鬼畜美学)
Author: Tetsuto Uesu
Illustrator: Tamago no Kimi
Akatsuki Ousawa was summoned to another world, where there is a Maou(demon lord). However, unlike most games or stories, he was not needed. There is already another hero in the world. In fact, they became friends. Things changed when Maou came to attack the city one day, and the hero sacrificed himself to protect Akatsuki. People condemned him for the loss of their hero. The world was brought into an age of darkness. Akatsuki left the city without a word...
Some time passed, and as the passed away hero's fiancee worked hard to rebuild the city that her late father, the king who too pass away then, Akatsuki came back, with enough strength to protect the people. The time he went missing was not in vain, he went into the deity realm to master a power so that he is capable of fighting back. He then led the people against the Maou and is worthy of being called a hero as well. Despite all his accomplishments, there are still those that resent him for the death of the ex-hero, and thus calls him a "Punk Hero", which he gladly accepts.
On the final night before the final battle, he sneaked into the Maou's castle alone. The battle raged, and a victor was born. With his dying words, the Maou entrusts his beloved daughter to him, asking him to bring her back to his world, where she would be safe, while at the same time end the meaningless war between the two races. Akatsuki thus leaves, with the daughter, leaving everyone behind, even the princess, who has also fallen in love with Akatsuki.
And so, Akatsuki returns back to his own world, bringing the Maou's daughter along. BABEL captures the dimensional rift caused during the dimensional travelling, and approaches the two. Perhaps a twist of fate? The Maou's daughter's name is very similar to his sister's and so Akatsuki gave the name "Muu"(is it?) to her.
A mission was given to Muu by the Maou, that she is to evaluate Akatsuki, and should he be unsuitable as a watcher or guardian, she should not hesitate into killing him. But interacting with Akatsuki made her have mixed thoughts, while at the same time she slowly understands that Akatsuki has intentions of taking on the entire world, as the name she bears is more painful than one could imagine.
Akatsuki's sister is dead, a long time ago, never to return. Thanks to Akatsuki's father and brother, who are in opposite ends of the world, one leading COCOON, the other the rebellion group. Just what can they achieve from a war that led to their own family's death? Akatsuki intends to challenge and beat the two greatest forces in the world to put an end to it once and for all...
Publisher: HJ Bunko
This series will soon have an anime
P.S Thanks to ShadowzeroHeart for the actual synopsys