WARNING: the following contains spoilers for Episode 3 of I've Been Killing Slimes for 300 Years and Maxed Out My Level, now streaming on Crunchyroll.
An overworked office employee finds herself reincarnated into a new fantasy realm after collapsing, and her new isekai adventure promises endless adventures and excitement. In theory. I've Been Killing Slimes' Azusa Aizawa, the Witch of the Highlands, is determined to take it easy for the rest of her immortal life, but trouble keeps knocking on her door, with Episode 3 adding elf girls to the list.
Already, Azusa has accepted Laika the dragon-girl as her new friend and apprentice, and she's about to make another friend, one who's on the run. Halkara the elf has drawn the ire of the great demon Beelzebub, and only Azusa can help her.
Azusa simply can't catch a break. Despite her best efforts, rumors and tales of her incredible magical power are spreading fast, and that means that troubled parties will keep seeking her for help. In this case, it's Halkara, an elf girl who ran an apothecary back home in the Hrant province, home of the forest elves. When she arrives on Azusa's doorstep, the witch only reluctantly hears her out. Halkara makes a highly effective energy drink called Nutri-Spirit, but the demon Beelzebub drank it and nearly died from poison. Now, Beelzebub wants Halkara dead, and only Azusa can protect her.
So, Azusa throws up a barrier around her home to repel Beelzebub (though an annoying fly keeps buzzing around). And, despite being wanted for 15 million gold coins, Halkara is determined to keep up her trade and invites Azusa along for some mushroom-picking and education. She even ingests a mildly poisonous aphrodisiac mushroom, forcing Azusa to use her magic to keep the lustful Halkara at bay and dispel the mushroom's effects. Later that night, though, the fun and games are over: Beelzebub has arrived.
That annoying housefly was no ordinary pest. It's actually Beelzebub's animal form, and she appears before Azusa's party in her humanoid f0rm, complete with horns and red eyes. What's odd, though, is that she has been drinking bottles of Nutri-Spirit behind everyone's back, and hardly seems affected at all. Azusa doesn't have much time to reflect on that, though; Beelzebub challenges her to a duel outside until she runs afoul of Azusa's barrier before being taken inside to recover. She's mildly sick but is determined to drink more Nutri-Spirit soon, despite the apparent danger.
Turns out Nutri-Spirit isn't poisonous to demons -- it's actually good for them and is mega-popular in the underworld, with even the Devil himself being a fan. The truth is that Beelzebub drank the potion to pull an all-nighter, but the stress of overwork caused her to fall ill. Azusa is grimly reminded of her previous Earth life but chooses not to comment on it. Instead, she accepts Beelzebub as a new friend, and Beelzebub cheerfully mentions that the underworld has been ruled by the same dynasty for several long centuries, so Azusa need not worry about more wrathful demons.
From this point on, Halkara can keep making Nutri-Spirit drinks in peace, and that may serve as an extra source of income to fuel Azusa's great project of slacking off for all eternity. If someone ends up in an isekai world for all time, they might as well have a fine drink in hand while they're at it.