Parallel World Pharmacy: Jesus was an Isekai
This is a cute little one-season "let's highlight the importance of a particular job/field" anime. And yes, it's technically a reincarnation isekai as well. The protagonist was, on Earth, a genius chemist/pharmacist/biochemist/surgeon - let's just say Doogie Howser and House have nothin' on this guy. He's world famous for figuring out how to treat previously untreatable conditions.
Unfortunately for the protagonist, he's SO smart and SO driven he works himself into a heart attack in his mid 30s, and dies. He wakes up in the body of a ten year old boy, in another world.
So far, standard isekai really. Except not quite. I don't know why they went all out on this aspect of the story, since it has nothing to do with why they created the anime (join the school of pharmacology! It's totally cool! We promise!) but this is where things went a little weird.
Firstly, he didn't just wake up in the body of a ten year old. This isn't the standard reincarnation isekai. He doesn't get overlapping memories of his childhood in this new world. No, our hero woke up in the BODY of the ten year old. Who hadn't been breathing FOR A SOLID HOUR. And the boy hadn't just bumped his head. He'd been HIT BY LIGHTNING.
He has glowing fern patterns on both his arms. Of course, protagonist is like "yeah, you get those when you get electrocuted" but no. Those fern patterns are the holy symbol of the Medicine God.
What follows, as a kind of consistent B-plot, is the people of this new world deciding very quickly that Our Hero is in fact the incarnation of the Medicine God, here in their world to save lives and upend medical science as they know it (which, since their medical science is roughly 14th century Europe, is good for everyone) and Our Hero trying and usually utterly failing to pretend that he's just a ten year old human boy.
This is, by far, the most hilariously fun part of this otherwise pretty quiet and serious anime. Because these people don't know what bacteria are, or germs, or viruses. Our Hero promptly invents the microscope to show them, but I have to admit I find it really funny that he's consistently saying things like "yes, this illness is caused by tiny invisible creatures" and everyone else is going "EVIL SPIRITS???"
Because y'know. "tiny invisible malevolent creture" and "evil spirit" do kinda sound like you're talking about the same thing. He's chased by the Inquisition for the standard isekai business of having basically infinite ultra magic and casting no shadow, but when he tries to heal the inquisitor that tried to kill him, they flip right around into OMG WE JUST TRIED TO EXORCISE A GOD.
(This one especially amused me, because the inquisitor he heals then goes on to get himself assigned to Our Hero's town...and present Our Hero with this really really cool staff. He doesn't tell OH until after he picks the staff up that oh, by the way, ONLY A GOD CAN TOUCH THAT STAFF - so, you know, you're a god, we proved it. OH then tries to sell the idea that okay maybe he's a god but an UNDERCOVER one, okay? Please?)
This little B-plot keeps up all through the story; the viewer knows the science (which is, btw, apparently really accurate; the series was written by doctors and chemists) but frankly, the common people of the isekai world's explanations with spirits and gods and demons actually work just as well to explain what's going on most of the time.
Oh and the Black Plague has an actual literal body. Walking around. So we're not just talking 'ignorant peasants' here. Sometimes they're right.
