Isekai by Moonlight

Isekai by Moonlight is a Sailor Moon isekai fanfic, written by Robkelk initially for fun and as stress relief... but the story grew in the telling to the point where it received the full preread-and-publish treatment.

Our ~~hero~~ protagonist, who we'll call "Robu-san" because practically everyone else in the story calls him that or a variant thereof, wakes up in Japan in a teenage body and with an initially unknown set of metahuman powers, and is told to transfer to the local junior high school... the same day that Makoto Kino (not yet Sailor Jupiter) transfers to the same school. '90s-anime Sailor Moon isekai ensues. He quickly realizes that, since he knows how the canon anime's story ran, he can change things until his changes make his knowledge irrelevant - but instead of waiting for a major plot point to start making changes, he goes ahead and starts changing minor things, knowingly invoking the Butterfly Effect without being able to predict whether doing so helps or hurts. Then Robu-san discovers why doing that was a bad idea.

And why was he set up to meet Makoto first, instead of any of the other Senshi?

Read it at the Drunkard's Walk forums (HTML) or on the author's website (PDF). As of late-June 2023, three chapters have been published; the writer has prepared at least a skeleton of an outline for the entire story.

Tropes used in Isekai by Moonlight include:

Adaptation Expansion and Compressed Adaptation: Yes, both apply. For legal reasons, the writer cannot simply re-tell the core parts of the original anime, leading to anything that's based on an original episode being compressed. But there are places where the original anime left room to add details, which the writer has taken advantage of to add scenes, characters, and entire subplots to the story.
Affectionate Nickname: The "True Companions" version. Robu-san calls Usagi "Bunny-chan".
Alien Sky: The first clue where the characters were sent during the "Sent to Another Dimension" story arc was in the sky.
Arbitrarily-Large Bank Account: Played with during the first chapter in that Robu-san's bank account has an upper limit, but any withdrawal he makes is replenished within a week. It isn't until the second chapter that he learns who's paying his bills.
Are You Pondering What I'm Pondering?: Downplayed during the "sent to another dimension" story arc, in a discussion about how to get home:

"Are you thinking what I'm thinking, Shario?"
"I think so, Rob, but where are we going to find a dimensional transit meister at this time of night?"

Ascended Extra / OC Stand-In: There's more to Urawa Ryou (who appeared in two episodes in canon) in this story than just "precog who likes Ami".
The Big Damn Kiss: Makoto and Robu-san, just before the Senshi take the battle to the Dark Kingdom. Bittersweet because she knows from him that she probably isn't coming back... and it's her First Kiss, too.
Asian Gal with White Guy: Makoto and Robu-san. Race isn't a factor in their mutual attraction, but the fact that Robu-san was a Sailor Moon fan before being transplanted into their world certainly helped.
Bread, Eggs, Breaded Eggs: Conversed. "Zoicite. Sewers. Rats. Zoicite covered in sewer rats."
Cliff Hanger: The end of the second chapter.
Cloning Blues: The "robot doubles" subtype, played with. Two of the synthetic-intelligence characters introduced late in the third chapter remember being the biological people that they were based on.
Cool Sword: Naru Osaka develops the metahuman ability to make swords in seconds when needed, but only if the raw materials are available. Since carbon is usually available, the swords often have diamond blades. Eventually the intimidation factor of making a sword out of "thin air" doesn't work against an opponent, and the character needs to actually learn how to fight with a sword.
Crash Into Hello: How Robu-san met Makoto.
Crystal Prison: Naru's only attack when she was a youma was to put Robu-san into one of these, with no way to breathe. Luckily for Robu-san, she's defeated quickly.
Darker and Edgier: The events of the Sailor V manga are included in the backstory of Isekai by Moonlight... which means that, unlike in the canon anime, Minako has blood on her hands.
First-Name Basis: A handy barometer as to who Robu-san thinks is important, and vice versa, in the story.
- Makoto goes to first-name-without-honorific basis before the end of the first chapter, while Rei remains "Hino-san" for the entirety of chapter 1.
- Robu-san remains on a family-name-with-honorific basis with Hino-san until the middle of the second chapter, when she gives him permission to call her Rei. They never get close enough to drop the honorifics.
- Robu-san, Makoto, and Ami are on a first-name-without-honorific basis by the end of the second chapter. Ryou joins that list partway through the third chapter, as do the friends they make while they're in Another Dimension.
Genre Savvy: Robu-san, his early blind spot about his relationship with Makoto notwithstanding. Early in the first chapter, he worries that "Stupid genre conventions" is becoming his Catch Phrase. By the end of the second chapter, it has.
Getting Crap Past the Radar: "my ... nosebleed." Context shows that this isn't referring to a literal nosebleed.
Ghost Memory: One of Robu-san's powers, which requires the cooperation of the person donating the memories, is to copy the other person's memories... and give them back later.
How Do I Shot Web?: Played With. Robu-san had no idea what his powers were until he used some of them reflexively to protect other people. Once he realized what his powerset was, though, he could use the powers without effort.
I Know You Know I Know: The "absolute honesty" version is used by Robu-san when he wasn't sure whether Zoicite was spying on him.
I Need to Go Iron My Dog: Robu-san points out an eye-catching rosebush in order to give Sailors Moon and Jupiter some privacy to transform back to Usagi and Makoto... and then Makoto points out that it's a poinsettia plant.
It's the Principle of the Thing: In the first chapter, Ichigo (who was not yet friends with the other characters) made a comment about Robu-san that he shrugged off... but Makoto verbally lambasted her for making it.
Literal Metaphor: At a picnic, Sailor Mercury eats like a bird after she learns how to fly, swooping down from the sky and grabbing a sandwich.
Load-Bearing Boss: As a security measure, the tunnel from D-Point started to collapse as soon as Kunzite died.
Man on Fire: Zoicite, when most of the Senshi attack him at the Star Light Tower. It doesn't last long.
Mauve Shirt: With the number of deadly enemies the Senshi go up against, you weren't really expecting all of the Original Characters and OC Stand-Ins to survive, were you?
Mathematician's Answer: Two of them, at the start of the "sent to another dimension" story arc.

"Has anybody figured out where we are?"
"Outside?" Makoto answered with a shrug.
"In an open field," Ami added

Neat Freak: Makoto, as in canon, but given a reason here that ties in with her parents' death.
The One Guy: Robu-san for part of the first chapter, when (as in canon) Tuxedo Kamen was kidnapped.
Original Characters:
- In the first chapter, Aoyama Ichigo in Makoto's class and Sato Kichirou in Robu-san and Ami's class.
- Introduced during the "sent to another dimension" story arc, Sakura, Ichiro, Meia, and Kasandara, and playing with the trope, Hayate-chan and Shario-chan.
New Transfer Student: Makoto (as per canon) and Robu-san (the same day) at the start of the story, Minako later, and Urawa Ryou in the second chapter.
Pop Cultural Osmosis Failure: Of the "Who's X?" variety, whenever Robu-san references or quotes from famous works that haven't been written yet.
Power Perversion Potential: Discussed and consequently averted:

Robu-san: So, Ami-chan, you want a teenage boy who you know can turn invisible to join you in a trip to an onsen?
Rei: Bad idea.

Reset Button: Robu-san lampshades in the second chapter the canon occurrence of this trope at the end of the first anime season and first chapter. In order for the canon timeline to make sense, it's a near-literal reset, winding the clock back by one year.
Sarcastic Clapping: One of Robu-san's favourite ways to draw attention to himself and away from the Sailor Senshi. The trope being unknown in Japan in the early 1990s, the clapping serves less as a psychological attack and more as a distraction.
Sarcastic Confession: During the months-long break between the first season and R that's mentioned in canon, when (in this story, most of) the Senshi don't have memories of being Senshi:

Robu-san: You see, Ami-san, Makoto and I are part of a secret team that defended the entire Earth from being conquered during the Missing Time, and the existence of the Missing Time is a side-effect of our success.
Minako: Pull the other one, it has bells on.

Secret Keeper: Robu-san for the Sailor Senshi, and vice-versa. Also, Osaka Naru by the end of the first chapter and Aoyama Ichigo midway through the second chapter for all of them.
Sexy Discretion Shot:

I closed the door behind me... and that is all that anybody will learn from me about the rest of that day, except that we were both very happy at the end of it.

Something Completely Different: The Whole-Episode Flashback story arc that starts when Robu-san, Makoto, Ami, and Ryou get sent to Another Dimension by the Black Moon's Stick and crossover with Lyrical Nanoha. Most of the senshi appear only in the chapter's first, short framing scene, and Mamoru, Naru, Ichigo, and Mizuno-sensei do not appear at all.
The Stations of the Canon:
- The story starts with the anime-only "Seven Great Youma" arc, and in the first chapter canon events are shown in the same order that they appeared in canon to show the inevitability of the canon season ending.
- And again in the "Doom Tree" arc, because - having ruined one canon relationship already - Robu-san doesn't want to take any chances that he'd end up derailing Usagi and Mamoru's relationship. Once Chibiusa shows up, The Stations of the Canon become less important.
Super Empowering: In the backstory for Robu-san, and in-story for Osaka Naru.
The Team Normal/Ordinary High School Student: Aoyama Ichigo, who isn't even a formal member of the team... but she isn't a Magical Girl Warrior or a Designated Victim, either.
Their First Time:
- As he promised, when she's finally old enough and they'd been dating for years beforehand. The act itself is kept off-screen.
- And then the other couple, two-and-a-half weeks later. Again, the act itself is kept off-screen.
Theiss Titillation Theory: He thinks his girlfriend looks sexier in a négligée than she does when she's naked during her Transformation Sequence.
There Was a Door: Justified:

Robu-san: By the way, there was a door.
Makoto: With a droid blocking it, darling.

Transformation Is a Free Action: Justified after Ami learns some magical theory and makes the Transformation Sequence instant.
Translation Convention: While the dialog is in Japanese unless otherwise noted, it is written in English, just like the rest of the story.
Unfamiliar Ceiling: The first two words of the story are "Unfamiliar ceiling." Robu-san quickly discovers that he's been rejuvenated, bringing the trope into play.
The "Unicorn In The Garden" Rule: Somebody is Trapped in Another World where abilities are gained and allies are found. (The third chapter repeats the same unicorn.)
Unusual Chapter Numbers: Chapter 1, Chapter R, and so on, referencing the source anime's season names after the first chapter.
Unwanted Harem:
- Discussed but never actually happens; it's pretty clear that First Girl Wins is in play instead.
- This applies to Ryou, Robu-san, and Mamoru; nobody has or wants a harem. No matter how many girls try to throw themselves at Urawa Ryou.
Wacky Marriage Proposal: Essentially a proposal in reverse – Makoto announces herself to someone she just met as Robu-san's fiancée, then asks him, "We are going to get married, right?" (He says yes.)
Watch Where You're Going: Done deliberately by Sailors Moon and Jupiter as part of their plan to convince Kunzite that they aren't getting along.
Waxing Lyrical: In order to give advance notice of his presence in one scene, Robu-san starts singing the opening theme to Princess Principal, gender-swapped where necessary.
What Year Is This?:
- One of the first things Robu-san asks himself. He gets the answer by turning on the TV.
- At the start of the "Sent to Another Dimension" story arc, discovered when the banished characters ask their hosts.
Writing Around Trademarks: The trope is mentioned by name the first time that Makoto and Robu-san stop at a (canon) 7-12 convenience store.
You Can't Fight Fate: Not during the first season, at least; everything Robu-san does other than forming relationships with various Senshi and their friends only accelerates the canon plotline. Canon starts going off the rails when Chibiusa shows up, and the second chapter ends with canon being broken completely.
You Did Everything You Could: Minako's opinion during the first talk she had with Robu-san after he was forced to kill a classmate.
"You?" Squared: Makoto and Petz during the Lucky Charms House incident, revealing that Petz had seen Makoto transform to Sailor Jupiter the previous time they met.