this is a Japanese series, it was written by Tappei Nagatsuki and designed by Shinichirou Otsuka. It has begun running since January 24th, 2014 till date and has been able to garner 19+3 side stories and 4 stories collections overall.
Hikkomori is a person who plays games. This is exactly what Subaru Natsuki does. One evening, having visited the convenience, he suddenly gets taken to an entirely different world. Without any prior knowledge whatsoever of the person who took him unknowingly, sooner enough, he made friends with a girl called Satella and another companion Puck. The former says her insignia was stolen by someone called Felt. And as soon as he and Satella got killed in a very mysterious way, Subaru woke up to the realization that he can return by Death which gives him the ability to get time reversed even at death.
He addressed Satella who got angry to be called by that name asserting that it denotes, ‘A Jealous Witch’ which was seen as a taboo. Through Reinhard in an entirely different timeline, Subaru guards Satella’s life from Elsa who is a renowned killer. She then opens up that her original name is ‘Emilia’ and in appreciation, Felt returns back her insignia. While recovering at Margrave Roswaal’s mansion, Beatrice takes back Subaru's mana. And after he is awake, he meets with ‘Ram and Rem’ and also Roswaal who contracts him as a Butler.
The latter explains that Emilia needs the insignia before getting qualified for his candidacy in the upcoming royal elections. When Subaru dies again he investigates the reason for his death as he attempts to reproduce the events leading to it. It was here that he realizes that he was cursed by someone whom he had deciphered to be one of the villagers he’d earlier on visited.
As a result, some creatures called Mabeasts threaten the village but Subaru and the twins have to help the villagers overcome the challenges. Much later, Emilia gets called to the capital by Wilhelm and Felix to Crusch’s camp whom are also part of the Royal Guards before the royal selection commences as Subaru and his group hooked up with the remaining royal candidate as Priscilla, Crusch, Anastasia and Felt; together with their knights Aldebaran, Julius and Reinhard. At first, Felt makes an announcement that she'll not be a part of the elections as Subaru proclaims himself as Emilia's knight. A fight ensued and Subaru gets seriously injured as he entered an argument with Emilia who took a decision to put an end to his relationship with him.
After Subaru has recovered, he decides to practise under Wilhelm and Felix admonished him to reconcile with Emilie. Rem informs that something is happening at the mansion and Subaru returns at the expense of the former’s pleadings. Over there, he realized many people are dead and was also gotten ambushed. Ram sacrifices herself so as to let Subaru be forced to run away as Subaru later reveals his ‘Return by Death’ qualities to Emilia whom cannot recollect who Rem was.
Later, Subaru and Rem had a fisticuff with the White Whale having successfully struck an accord with the causes of Crusch and Anastasia. Wilhelm then kills the White Whale getting a revenge for his wife's death.