Digital Devil Story

The original source material for the Shin Megami Tensei series and all of its many derivatives, Digital Devil Story is a trilogy of novels written by Aya Nishitani. Written in the late 1980s, there are three books in the series: the eponymous Megami Tensei (Reincarnation of the Goddess), Warrior of the Demon City, and Demise of the Reincarnation. The first novel was soon adapted into an anime and billed with its own name, as opposed to the series name.

In Jusho High School, the student body is divided into two groups: the gifted class and the normal class. One day Akemi Nakajima, one of the gifted and something of a maverick within the school, has the bad luck of being targeted by the semi-delinquent normal Kondo Hiroyuki. The reason? Nakajima had rejected Kyoko Takamizawa's advances, and in a fit of petty vengeance, she manipulated Kondo's crush on her to deliver Nakajima a vicious beating by proxy.

Humiliated and infuriated by the injustice, Nakajima goes about getting his revenge. Everyone knows that Nakajima is an ace programmer, but there's one thing no one knows: he's also an amateur magician. He had previously stumbled into the revelation that magic and programming were more or less the same, and had been building a Demon Summoning Program in his spare time. He'd never intended to use it... until Kyoko and Kondo provoked his rage. What follows is a disaster that can only gets worse before one can even hope that it will get better...

As you might expect from the original source material for the Mega Ten franchise, Digital Devil Story sets the basic foundation for the games that followed. That means it's happy to explore arcane lore even as it jumps into places that will make the average reader wish for some Trope Co Brain Bleach.

The novels were never released in the US. However, a dedicated English translations of the first two novels can be found here, along with a greatly improved English edit found here and here. A French translation was also done here.

Tropes! Come forth!

All Myths Are True: You should know this by now.
Attempted Rape: Poor Yumiko has to endure this. As does Izanami.
Beauty Equals Goodness: Yumiko.
Beware the Nice Ones: Yumiko's sweet, mischievous, a really fun girl. She's also the reincarnation of Izanami, and teaches Loki a thing or two about the efficacy of fire.
Big Bad: Nakajima seems like he's heading this way at first. Loki takes that role from him. Set assumes this role after Loki's death, and holds on to it for the second book. Lucifer himself takes the role in the third.
Bitch in Sheep's Clothing: Kyoko. She doesn't get to enjoy it for very long.
Classical Mythology
Clingy Jealous Girl: Ohara. She snaps Yumiko's neck out of jealousy, right before Loki would have raped Yumiko.
Chekhov's Gunman: Charles Feed is mentioned in passing in the first book. He becomes a major supporting character in the second.
Crossover Cosmology: In the first book alone, we have Loki, Izanagi, Izanami, Yomotsu-Shikome, and Set.
Dark Is Not Evil: Kerberos is more like a loyal oversized puppy to Nakajima.
Deal with the Devil: What sets everything in motion.
Determinator: The main protagonists can be very stubborn about giving up.
Disproportionate Retribution: Kyoko has Kondo beat the crap out of Nakajima because he rejected her. Nakajima summons Loki and has the demon consume Kyoko and Kondo's souls.
Dude Looks Like a Lady: Nakajima. The narration specifically mentions he takes after his mother. Used by Kyoko as a taunt.
Earn Your Happy Ending: For the first book, at least.
Evil Is Not a Toy: Loki teaches Nakajima this lesson. Painfully.
Eviler Than Thou: Loki quickly disabuses Nakajima on who runs who.
Fan Disservice: The loving care with which Loki's...activities are described can result in Squick.
Fan Translation: Only way the English-speaking world is ever going to read these. French-speakers too.
Functional Magic: Thaumaturgy and other real world magicks.
Gone Horribly Right: Using you ace progamming skills and amateur wizard talents to create demon-summoning software? What Could Possibly Go Wrong??
Heel Face Turn:: Nakajima.
Heroic BSOD: Nakajima suffers this after Loki betrays him.
Heroic Sacrifice: Yomotsu-Shikome dies facing Loki in order to buy Nakajima enough time to revive Yumiko.
Hot Shounen Mom: Nakajima's mom. When she's out with Nakajima, they get mistaken for siblings!
Hot Teacher: Ohara.
Infinity+1 Sword: The Japanese god of fire Hi-no-Kagutsuchi is turned into one of these.
Jerk with a Heart of Gold: Nakajima.
Jerkass: They abound. Kondo, Kyoko, Nakajima for most of the first book...
Jerk Jock: Kondo. Like Kyoko, he doesn't get to enjoy it for very long.
Kill the Cutie: Yumiko. Twice.
Love Hurts: Yumiko knows this quite well. Ouch.
Metaphysical App: The protagonist of the original Digital Devil Story novels creates a computer program to duplicate demon summoning rituals. It quickly becomes a case of Gone Horribly Right when he uses it.
Mons: Expected, since it's Mega Ten's source. Nakajima has two: Loki and Kerberos. After Loki's betrayal, this is reduced to one.
Magic From Technology: By realizing the similarity between structured summoning rituals and programming algorithms, Nakajima wrote the Demon Summoning Program. And was horribly successful.
Naughty Tentacles: One of Loki's powers.
- Although they're more like Combat Tentacles because he uses them to crush people and absorb their blood.
New Transfer Student: Yumiko. Too bad it had to be into Josho High...
Nice Job Breaking It, Hero: Nakajima. Sure, he successfully develops the Demon Summoning Program. Unfortunately, he failed to build in proper safeguards that would impose a contract on a summoned demon. Loki turns on him very quickly, resulting in the deaths of at least half his classmates, as well as many innocent bystanders. To top it all off, after Nakajima defeats Loki, Ohara ends up summoning Set, the most powerful evil god of ancient Egypt. As icing on the breaking cake, Many demons have sensed the pathway Nakajima opened to their world, kindling their ambition to conquer the human world. More than just a handful of those demons want to ally themselves with Nakajima.
- The ending of the second book isn't any better. Sure, he beats Set and saves the world, but he also unwittingly allows several demons to escape from Atziluth by insisting that he has to save Yumiko.
No Export for You: This is Shin Megami Tensei's source material. Goes without saying it will never see the light of day outside Japan (except in fan-translations).
Orphaned Series: Or more like orphaned translation project since the translator hasn't been working on it for years.
Powers as Programs: Nakajima successfully builds a Demon Summoning Program, and also develops a Demon Transfer Theory which gives demons virtually free range.
Reincarnation: The main characters are the reincarnations of Izanagi and Izanami.
- In the second book Special Forces agent Narukawa is the reincarnation of Tsukuyomi.
Red Shirt: A segment in the first book and several segments in the second book go into absurd detail about the lives of minor characters. The segments usually end with them slaughtered by Loki/Set.
Sex Face Turn: Reversed version. as it's Ohara who does this, it also counts as a reverse High Heel Face Turn.
Sliding Scale of Idealism Versus Cynicism
Star-Crossed Lovers: The main protagonists have this in spades.
Summon Magic: The Demon Summoning Program.
Teacher-Student Romance: This is what Yumiko originally thought was happening between Ohara and Nakajima.
The Dragon: Loki enters as Nakajima's dragon. Ohara gets promoted to Loki's Dragon soon after.
- In the second book, Isma Feed serves as Set's Dragon.
Urban Fantasy: Set in Tokyo, there are demons running around, Solomon Crests, thaumaturgy... yup, it qualifies.