Ex.ReZero x KonoSuba Crossover!/Synopsis

God's Blessing for The Pretty Maid!
Returning to his mansion, Kazuma is bewildered to find a timid and pretty blue-haired maid in the living room, before he is chided by a fatigued Megumin laying on the couch for not carrying her back home from her daily Explosion. As Kazuma talks of the mayonnaise he had bought for cooking dinner, the maid muses over this world also having mayonnaise, which an acquaintance of hers likes, and makes Kazuma aware of her possibly coming from another world.

Megumin then introduces the maid as Rem, who had appeared soon after she cast Explosion. After Kazuma rebukes Megumin for going off for Explosions alone, in which nobody would have been around to carry her immobile body back if not for Rem passing by, Megumin explains that she was only scouting for a target that day, but ended up casting the spell when she found herself enveloped by a white mist. Rem next recaps how she simply went out to buy the bag of Appas in her hands, yet found herself seeing the collapsed Megumin upon a white mist engulfing her.

Wondering if the lost Rem had been spirited away since she is apparently unfamiliar with Axel, Kazuma offers to ask the Adventurer Guild for help with investigating any magic or monsters that can control mists. Thrilled at having a beauty who isn't insane being around, he next invites Rem to stay at his mansion for the time being, much to her relief. And thus they start life with this pretty maid, who is slightly lacking in the common sense of this world, as shown when she expresses puzzlement at being asked if her Appas will attack people.

Rem turns out to be an early waker who starts preparing the party's breakfast before daybreak, and apologises for waking up late when she mistakes the Kazuma who had stayed up all night as getting up earlier than her. Confessing to the apologetic Rem concerned with his health that he had been playing games all night instead of researching the white mist, Kazuma feels elated at having a "pretty girl flag" raised in what an other-worldly life should be like, though his enthusiasm dies down once Rem bashfully talks of Subaru.

On top of her numerous chores, Rem finds herself also having to serve afternoon tea to a fussy Aqua, who Kazuma quips as merely pretending to understand tea. After Darkness expresses their openness for Rem to join their party, Kazuma asks about Rem's origins, to which Rem lists out locations like Lugunica, Vollachia, and Kararagi that the party hadn't heard of.

Megumin accordingly returns from the Guild, and promptly suspects Kazuma of sexually harassing Rem, before reporting about rumours over previously unseen monsters appearing around Axel, which are so strong that people are refraining from going out. Asking Megumin and Darkness to continue their investigation around town and among the nobility, Kazuma heads to the scene for checking out the monster.

Soon afterwards, the Giant Toad chasing behind a panicking Aqua is smashed by the morningstar of Rem, who is stronger than Kazuma expects and at whom the weeping Aqua grabs onto for safety. Refraining from revealing where the morningstar came from, Rem finds the toad commonly seen around Axel not smelling of witches, to Kazuma's puzzlement. But as Aqua sprouts nonsense over the monsters headed deeper into the forest for better food because uncooked toads are smelly, Rem whose cooking she wants to go enjoy back home smells something.

A few days later when Darkness is out performing investigations, Rem spoon feeds lunch to Megumin who is immobile after that day's Explosion, while Aqua who had played boardgame with her the whole night is still fast asleep. Upon Kazuma advising Rem not to pamper the girls into uselessness, Megumin who reminds Rem of her sister chides him for his jealousy. As Kazuma stares at Rem in a way that disturbs her when hearing about her sister's antics, he hears her comparing his jersey to that worn by Subaru, the description of whom appears to be a weak hiki-NEET reincarnate without particularly strong abilities just like he is, and unlike him who has an Aqua capable of Resurrection may very well draw curtains upon dying. Although feeling a little empathetic towards Subaru, Kazuma who Rem mistakes for liking him quickly retracts his feelings of friendliness for Subaru once hearing of girls such as Beatrice and Petra also being fond of him. Megumin thus offers to be an older sister role for Rem to cuddle up to, and Kazuma's gibe at Megumin over her looking more like a younger sister unexpectedly makes Rem smile.

Rem later panics when the Bell Peppers she was trying to cook turned out to be feigning dead before attacking once her back was turned, so Kazuma confirms with Rem over her origins from another world, though he keeps the fact of Subaru also originating from his world secret. While Rem is again concerned with Subaru worrying about her absence, Darkness as Kazuma expects bursts in proclaiming of her accepting a quest for hunting the dog-like monsters that had appeared around Axel along with the white mist.

Subsequent to the trio rendezvousing with Aqua and Megumin at the forest where the monsters made their lair, Rem upon seeing the Demon Beasts turns all ruthless as she casts El Huma to slay a bunch before bludgeoning at the rest with her morningstar, scaring Aqua so much she wishes to leave before Kazuma stops her. The boss of the Demon Beasts however charges straight at Kazuma's party, at which Darkness jumps out to stop it only to get bitten. Initially trying to cover for Rem with his bow and arrows, at the maid's directive Kazuma changes to aiming for the Demon Beast attacking Darkness who is enjoying being squashed under a beasty dog, yet the Demon Beast manages to dodge the arrow and disappear into the woods. After dispatching the rest of the Demon Beasts, Rem who doesn't mind Darkness' perversions due to serving Roswaal discovers in horror that the bite was cursed. But just as Rem proceeds to go hunt that Demon Beast down in order to save Darkness' life, Aqua casts Sacred Break Spell to dispel the curse in a replication of the previous occurrence, following which Darkness and Megumin try to comfort the embarrassed Rem, although Aqua's comment on her actually having a kind personality renders their efforts moot.

His gamer's intuition telling him that Rem can return to her world once the remaining Demon Beast is dispatched, Kazuma using Enemy Detection leads the hunt in place of Rem who cannot detect the weakened smell of Witches on the monster. Locating the Demon Beast which had scared away the weaker monsters in the vicinity, Kazuma instructs Megumin to finish it with an Explosion, though Aqua despite Darkness' restraining objects to having Rem who pampers her go back. As Rem expresses her gratitude to the others, Kazuma hands her a sealed box of Apples as payment for her maid services so she can go and make Subaru some Appa pie. But just as he wishes Rem to live happily with Subaru, the maid reveals that she is aiming to become the second wife because Subaru is in love with Emilia. Becoming insanely jealous at Subaru owning a harem, Kazuma tries to stop Megumin from completing her spell so he can make Rem a part of his party, yet because of Darkness' obstruction can only helplessly look on as the Explosion is cast.

God's Blessing for This Wonderful EMT!
Waking up on a chair within a white room, Emilia is told by a blue-haired beauty sitting in front of her that she had died from choking on mochi, before cracking up over the cause of death common to the elderly, which according to records the half-elf counts as one of. As Emilia stares incredulously at the girl who introduces herself as w:c:konosuba:Aqua the goddess usually in charge of processing the young dead from Japan, Aqua skips right to the part where the deceased can be granted reincarnation to another world with the original memories and abilities intact.

Unlike Kazuma who immediately agreed, Emilia being from an another world herself needs a 30-minute long explanation before she finally grasps the concept, with Aqua hard-selling her to accept through promises of special cheat items upon reincarnation, though the goddess throws a small tantrum upon finding these supplies and equipment that were provided for w:c:konosuba:Eris being superior to those she used to work with. As Aqua hurries Emilia into picking a cheat item from the catalogue while Eris is gone so that the Demon King can be defeated and her way back to the Heavenly Realm assured, the still-confused Emilia who cannot contact Puck agrees to the reincarnation deal, to the joy of Aqua.

When helping Emilia go through the selection of cheat items, however, Aqua finds flaws with every one on the catalogue, and Emilia feeling herself unsuitable for using them anyways chooses Aqua to be her special cheat item so that somebody will be able to guide her, to the utmost horror of the goddess. A white magic circle subsequently appears around the pair, which Aqua panicking at history repeating itself unsuccessfully tries to escape from, before they are both transported away.

Finding herself sent by a magic that she makes comparisons with Beatrice's Door Crossing to the middle of a busy town street somewhat different than Lugunica, Emilia notices the teary Aqua beside her in a state of panic which soon develops into a full-fledged quarrel. Upon noticing bystanders looking at them, Emilia tries unsuccessfully to cover her elvish ears, followed by Aqua dragging her into an alleyway, where she berates Emilia for being the second person who brought a goddess into this world.

Aqua next redoes her hairstyle into a braid in addition to putting on glasses to prevent identification by acquaintances in this world who may chide her, then shows Emilia how there is no need for her to hide her half-elf identity in this world where Elves can freely walk around on the streets. Still unsure, Emilia asks a rough-looking passerby if he is afraid of her, much to Aqua's amusement. The man on his way to the Succubus Cafe was initially wary of a scheme to swindle his money, but upon seeing Emilia's pained eyes, decides to call her beautiful instead. After the overjoyed Emilia drags Aqua away with a strength comparable to Darkness, the man decides to request dreaming about a blue-haired girl with glasses instead of defiling the pure girl with silver hair.

Happily walking the streets of Axel the Town of Beginners without the need to cover her ears, Emilia who joyfully praises Lady Aqua pleases the goddess of water so much she is rewarded with a display of Create Water, though when she asks for strolling around longer, Aqua who had chased Eris off so she can secretly send more reincarnates to this world instead goads her into quickly heading to defeat the Demon King. Seeing Emilia's disappointment, however, Aqua who finds Axel pretty much like how she had left it agrees to show her around.

Soon describing Axel as lacking specialties, Aqua proposes going to Arcanletia where the Axis Church that worships her is located, but Emilia who refuses to convert feels content with looking around Axel with Aqua, before being treated to some food from stalls and taken to the Adventurer Guild where she can register as an adventurer.

Arriving in front of the Guild building that has a combination of bar and dining hall, Aqua explains how upon registration she will be handed an Adventurer Card, according to the stats on which she can select a Class and then head off as an adventurer to fight the Demon King. The pair of beautiful girls draw a lot of attention from the male adventurers inside upon their entry, to Emilia's discomfort. Yet once they head to the registration counter, the receptionist lady recognises Aqua due to her Adventurer Card, prompting the other adventurers to lose interest and leave, following which Emilia's registration fee is recorded on the sorrowful Aqua's tab.

Later given an Adventurer Card that she somehow knows how to read, Emilia who is registered as an Arch-Wizard is advised by Aqua not to learn only one spell like Megumin does, though she is befuddled over Aqua's recommendation of using her skill points to learn Party Tricks. Still unable to detect any spirits and concerned about making Puck and Subaru worried with her absence, Emilia is encouraged by Aqua to quickly learn other magic after leveling up, and becomes impressed at the bulletin board posting quests for hunting monsters when Aqua proclaims knowing Healing Magic and Resurrection Magic. The praised Aqua accordingly gets carried away, and makes the flag statement of wishing for high-level quests like the previous ones against the Demon King's Generals or the Destroyer, which is immediately followed by an emergency broadcast from the Guild asking all the adventurers to assemble at the town gate, despite it not being Cabbage season.

Just like what the receptionist lady tells them, a giant version of the Giant Toad known as the Greatful Giant Toad that is the biggest of the century approaches the town, stunning the gathered adventurers since its bulk is the size of a small mountain. Initially hopeful at Kazuma being able to think of a way out of it, the other adventurers soon descend into despair upon Aqua telling them he and the other party members had gone somewhere far off, and further so when Aqua admits her inability to Resurrect people who get swallowed and digested. Despite Emilia becoming the only one discussing tactics with Aqua, her ideas of clashing head-on disturb the goddess, until she remembers Emilia being able to use Ice Magic.

With the other adventurers impatiently observing, Aqua casts Sacred Create Water to conjure a flood outside town, which because of the closed town gates are set gushing towards the GG Toad. As the humongous amphibian is slowed, Emilia following some chanting unleashes a spell powerful enough to rival Aqua's, which freezes the flood waters along with the GG Toad. After Aqua boasts of how she and her muttering devout follower had achieved a scaled-up version of what Kazuma had once did using Basic Magic, the GG Toad crumbles into frozen pieces.

Subsequent to Aqua and Emilia being lauded as heroes and having a taste of the toad meat before receiving their rewards, the two of them happily walk along the nighttime streets, when Aqua's junior goddess Eris comes berating her for snatching away her job while she was gone. Aqua though retaliates by calling Eris out for slacking off, and after being introduced to Emilia, Eris reveals that Emilia is actually still barely alive despite her soul being forcibly dragged to this world by Aqua, since that other world's records regarding life and death are convoluted and full of errors. Although Emilia is relieved over her being able to go back to Lugunica and the Roswaal Manor where she can see Puck and the others again, Aqua expresses her reluctance to let Emilia stop adventuring and return to a place where she has to cover her ears. Emilia though apologises for refusing Aqua's offer to persuade Kazuma into letting her join the party, so Aqua sadly defrocks her.

After Emilia is back in her world, Aqua accepts the erasing of Emilia's memories in this world for preventing bad influences over there. Eris who agrees to cover up for Aqua then consoles her, though Aqua starts bragging about the blessing she had gave to Emilia.

Regaining consciousness to see Subaru who had made the mochi looming over her in concern before Puck kicks him, Emilia tells them how during her coma she had a long dream despite not remembering what it was about. She next asks the two of them to look at her hand, before casting Nature's Beauty to happily spray the surprised pair with water.