Re zero spoilers

arc 1:
ubaru randomly appears in another world and instantly falls for a silver-haired helf-elf girl who was the only one nice enough to help him out. Here Subaru gets slightly acquainted with the world and learns he has an ability he names Return By Death where when he dies, he starts all over from zero. He meets many people from a giant named Old Rom taking care of a street urchin named Felt, to the strongest knight in the country and possibly the world named Reinhardt.

The problem with this arc is that a very skilled and very sadistic assassin is after an object very important to the silver-haired girl and she and Subaru die trying to get it back. He doesn't question what the object is and only wants to help out the girl who was nice enough to help him out and is willing to die for it. After trial and error, and with a lot of luck, he manages to pull in Reinhardt to deal with the assassin, but suffers near-fatal wounds even in the successful loop. The only reward he asked for before passing out was the silver-haired girl's real name, which is Emilia. Afterwards, Emilia tries to provide emergency treatment on Subaru and Reinhardt takes Felt with him for some reason.

arc 2:
Subaru wakes up in unknown room alone and decides to figure out where he is, when it turns out he's he's stuck in a endless, looping corridor. He eventually stumbled across a little girl who was apparently the one who healed him. She dislikes Subaru's attitude so she drains his mana (painfully) and he passes out, once again waking up in the same room but this time being watched by the twin maids Ram and Rem.

He learns that Emilia had brought him to her sponsor's mansion in the country side in order to treat him. He greets the mansion's owner and Emilia's sponsor, Roswaal, the royal court magician who speaks in a silly way and wears heavy cosmetics resembling a jester's. Subaru learns that the item Emilia was after in the first arc was a symbol of proof that allowed her to be a candidate to be the next ruler of the country, since the previous royal family including relatives have all died off to a strange and incurable disease.

Subaru, having no real plans having just come to this world, decides to work as a butler for Roswaal to stay with Emilia. Subaru begins learning how to read and write the new world's language under the tutelage of Ram, how to clean/be a butler (he's really bad it), general magic knowledge (he has an aptitude for dark magic, but can only use all his mana to more or less blind himself and a little of his surroundings. This is fairly useless since using all your mana means you pass out), getting bit by the village dog, playing with the village kids and doing morning exercises with them, getting to the know the mansion's residents, etc. He doesn't get too acquainted with Roswaal as he leaves early for business.

But one day after going to sleep, he wakes up in his room again being watched by the twin maids, this being somewhat unusual but not enough for Subaru to mind, he talks to them normally. They're somewhat taken aback by his over-friendly demeanor as they don't recognize Subaru. Subaru realizes that he had died in his sleep somehow and that his loop ability had created a checkpoint to return to for some reason. Subaru, now paranoid that death is lurking around the corner, tries to figure out what happened and more or less repeats everything. On the same night that he died in the first loop, he starts feeling very cold and weak, and it quickly gets worse. Despite his condition, he's worried about Emilia and goes to see if she's suffering from the same thing, but is killed by someone before he can get there.

Subaru begins to changing his actions a little. Like instead of working for Roswaal, he decides to leave the mansion to watch it from afar to see what the deal is. This time he hunted down and heavily injured by Rem who for some reason deemed him a threat without consulting Roswaal or Ram, and then finished off by Ram who caught up and pity-killed Subaru.

Subaru at some point loses it because the only one he thinks he can trust is Emilia and decides to hole up in his room in a loop. Eventually something happens and Beatrice (the little girl who healed him and the cause of the looping corridor) convinced him to come out, and Rem is found dead from the same thing that was affecting Subaru in the first two loops. This causes Ram to completely lose it and start going after Subaru because she thinks he has something to do with it, but he is protected by Beatrice and he runs away. He gets hurt somehow, mauled by a wolf or something, and he wakes up after Beatrice has healed him. Beatrice, despite her cold and tsun-tsun attitude, really doesn't like it when people are hurt in front of her. Eventually Ram finds them, still not having given up. After some talking (if you want to use that word for it) Subaru decides that this loop is irredeemable and throws himself head-first off a cliff, killing himself for the first time. Before he does, he lets Ram know that he in the end he likes her and everyone at the mansion.

Eventually he finds out that the reason Rem had attacked him was because each time he loops, Subaru reeks more and more of the same scent of the Witch of Envy. The Witch of Envy is a legendary evil witched, sealed by the 3 sages and the cause of discrimination toward Emilia. The witch apparently was a half-elf with silver-hair, just like Emilia, but was sealed like 400 years ago by the founding dragon of the nation, the holy swordsman, and a sage. Rem and Ram were of the Oni tribe, and Rem distinctly remembers the witch of envy's smell being there the day everyone was killed, but all this means to Subaru is that getting Rem to trust him is near impossible. Ram apparently can't smell it because she lost her horn as an Oni, making her more or less a normal person. Rem considered Ram losing her horn to be her fault and due to this, is extremely obedient to Ram.

At some point Subaru tries to tell Emilia that he can Return by Death, but when he does black arms appear and seemingly stop time, and cause him extreme pain. He literally can't tell anyone about it. He also later learns that by doing this, the Witch's scent grows stronger on him each time.

Eventually, Subaru figures out the cause of the curse killing him and Rem was the dog that keeps biting him in the village (the curse activates when the monster dog gets hungry, which can take up to a few days) and that several of the kids from the village have gone missing. Subaru goes into the forest to find them, along with Rem who is there to serve as Subaru's executioner if he does anything funny and a drug to help restore his mana after he uses Shakma (the blinding spell that costs all his mana). They find all the kids but one and Subaru has Rem take them out, since being an Oni she has super strength and Subaru couldn't even if he wanted to.

While she's evacuating the kids, Subaru finds the last kid and ends up fighting a wolf, abusing the drug medicine, and eventually getting mauled by several more wolves but is saved by Rem. He wakes up again after treatment for the nth time, but this time it hasn't looped; he's covered in scars all over from the severe mauling he got. He learns that he probably doesn't have long to live since the multiple curses from the dogs are too tangled to be removed and the curse will activate whenever they get hungry. Subaru is more concerned about Rem missing, though. Ram and Subaru quickly learn that Rem acted on her own again just like when she went to hunt Subaru in and earlier loop, so they head into the forest to get her since Ram has a clairvoyant ability and can find her. As they thought, Rem is hunting wolves to try to get rid the curse because she feels bad but there's simply too many and they don't know which ones actually cursed Subaru.

Ram runs out of mana along the way and ends up getting carried by Subaru. Rem is in her Oni-mode, meaning she's not very sane but a lot stronger, which Ram deems they need to hit the horn to bring her out of it. Rem tries to kill Subaru in her madness, but refuses to hit Ram for some reason. Subaru uses this by tossing Ram at Rem (after having Ram promise she won't get angry at his plan) and hits Rem on the horn, causing her to collapse.

Both Ram and Rem are exhausted, but Ram becomes able to move yet now Rem can't. On their way of escorting the twins out, wolves attack them and Subaru decides to play bait (by abusing the fact that he can't talk about Return by Death, although this is a very painful way of being bait) since the wolves are attracted to the Witch of Envy scent coming from Subaru. He abuses Shakma and the mana drug a lot more here and when eventually becomes unable to move. He gets saved by Roswaal returning, who then proceeds to clean up the rest of the forest of wolves while he was at it.

Rem now really likes Subaru, but Subaru's constant abuse of his mana gate (the source of mana inside of everyone) caused it to fracture, which means his mana regeneration is now worse than ever, using Shakma any more will only cause this fracture to worsen, and having a fractured gate is eventually lethal. But hey, look on the bright side, Subaru now has a lot, and I mean a LOT of cool scars to show off.